Here is the first DLC idea.
Those Who Hear The Winds and Those Who Ride The Seas
The Wind Bearers
From "http://www.uesp.net/wiki/Lore:Children_of_the_Sky" :
The further north you go into Skyrim, the more powerful and elemental the people become, and the less they require dwellings and shelters. Wind is fundamental to Skyrim and the Nords; those that live in the far wastes always carry a wind with them.
The DLCs would at first focus on an ancient brotherhood of Nords, the Wind Bearers, living in the far northern wastes of Skyrim. They are worshippers of Kyne and http://www.uesp.net/wiki/Lore:Jhunal#Jhunal, and follow the Way of the Voice with the help of the Goddess of the Storm, independantly of the Greybeards. They have a very close, primal relationship to Winds. Not ordinary winds, but conscious, bodiless, ethereal creatures. Neither animals nor vegetals. Winds and wind bearers are hunting brethren. A wind bearer could see, smell and hear far, through his wind. He could travel fast in it, become a wind and entwine his flows to those of his wind for short times, ask his wind to transport his voice, or blow his enemies away.
The DLC would also introduce a new race of Ada (or lesser), the http://www.uesp.net/wiki/Lore:Varieties_of_Faith..., noble, deeply natural nymph-like females who help the Wind Bearers to weave their relationships with Winds.
The player would also dicsover that http://www.uesp.net/wiki/Lore:Opusculus_Lamae_Bal_ta_Mezzamortie, the Blood Mother of Vampires, was a Daughter of Kyne, or a daughter of a Daughter. As the Wind Bearers' minds are very open to WInds, they are especially sensitive to the Shrieking Winds spawned by Lamae. Those foul Winds corrupt their soul and their su'um, leading to perverted, powerful, despicable thu'ums.
You would follow the Way of the Voice with the help of the Daughters, and then help them to rid their lost sister, Lamae, of Molag Bal's curse and heal her. But when you would finally face the Blood Matron, you would have to face dreadful opponents : enslaved Wind Bearers, corrupted by a Shrieking Wind, using the blasphemous Shriekings instead of Shouts, and would have to choose between the easy way : killing his opponent, and the not so easy way : breaking his connexion with the malevolent Wind. Alas, Lamae has taken advantage of the fight to flee away...
The Lords of the Seas
It would then be revealed to the player that Lamae actually left Tamriel. She's somewhere where the Winds of Kyne can't stroke her skin, and thus is out of grasp for the Daughters. Probably in a cave, or underwater.
Shortly afterwards, you would be contacted by a ship owner, who has heard of your new mastery of Winds, and who's willing to pay much for favorable weather during the navigation. The Dragonborn would then have to join a faction of his choice, and ride the Sea of Ghosts. Among the factions could be a pirate band (for example, the Blackblood Marauders or the Blood Horkers, or even Velehk Sain's band), the East Empire company, the new fleet of an ambitious merchant, or the Seafarer's Guild, a faction of explorers funded by Solitude, or even military fleets bound to the Empire or the Stormcloaks.
Each facton would offer its own missions, some involving naval battles, but whatever you chose, you'll increasingly hear of strange phenomenons, and dangerous waves, and ships which disappear. People of Winterhold fear the coming of a new Great Collapse. http://www.uesp.net/wiki/Lore:Yngol_and_the_Sea-Ghosts, the ones who killed Yngol, reappear...
During one of the missions, your boat would be caught in a surnatural mist, shaken by a dreadful storm generated by Shrieking Winds, attacked by something very BIG, and sunken. You would fall unconscious and wake up, naked but for a magical bracer made with coral, in an underwater cell. This brace allows you to breathe underwater, but reduces all your abilities, and you can't take it away.
You're in the http://www.uesp.net/wiki/Lore:36_Lessons_of_Vivec,_Sermon_1. The underwater kingdom of the Dreughs. You would discover that a faction of Molag Bal worshippers now rules over the society of Dreughs. As a slave you have to take part to the construction of war engines that the Dreughs are making to attack the unaware Skyrim. You would discover thier complex civilization, and its factions. There are the http://www.uesp.net/wiki/Lore:Lamia#Lamia, ancient enemies turned into slaves, the Gifted, who once were chimers, followers of Seht, but were offered gills and hermaphrodism by the Dreugh eagerness to carry experiments on bodies.
You'd discover that Lamae and her lover, the King of Dreughs, rule the Kingdom, but would also discover an underground faction of dissidents, the Sotha, worshippers of Azura. They claim to be the last remnants of the http://www.uesp.net/wiki/Lore:Great_Houses#House_Sotha. They'd ask you to perform sabotage in the Dreugh underwater shipyard, after which you'd be exfiltrated by a Gifted, and brought to the a Chimer underwater, hidden fortress. The Headquarters of the Sotha are inhabitted by Chimers, Sotha, Lamiae and dissident Dreughs, and warded by http://www.uesp.net/wiki/Lore:36_Lessons_of_Vivec,_Sermon_36, which are amphibious animunculi made by http://www.uesp.net/wiki/Lore:Seht.
You'd then have to get rid of your bracer, find a way to get your owned stuff back, freed your crew from their enslavement, and help the Sotha to rid the Castles of Glass and Coral of the dark influence of Bal.
It might end in a titanic (without intended bad pun) fight against a half-Daedric Kraken, the first born of Lamae Beolfag, spawned by her [censored] by http://www.uesp.net/wiki/Lore:36_Lessons_of_Vivec,_Sermon_28 (which is actually the very big thing which attacked your boat).
Here is the second DLC Idea.
Shezarrine -- The Road of Talos
Necromancy
The player would learn that there's a surge in necromantic threat. He could either join a Necromancer's faction or the Stendarr Vigilantes. Either way, he'd discover that the Necromancers are based on http://www.uesp.net/wiki/Lore:The_Exodus, a concealed Island in the Sea of Ghosts, which was the personal graveyard of Tiber Septim. Whichever faction you chose, you can't learn much about the Necromancers' leader yet.
There, you'd learn that the Necromancers are trying to uncover a terrifying secret. A soulgem able to capture the souls of Dragons. To discover it before the Stendarr Vigilantes/Necromancers and the Thalmor, you are sent to http://www.uesp.net/wiki/Lore:Alcaire. There, you get some clues about the mysterious http://www.uesp.net/wiki/Lore:Tiber_Septim Talos of Atmora/Hjalti the Early-Beard of Alcaire. An ancient book mentions "the Place where the Oath was Broken". Alas, obtaining the book isn't done without violence, which results in a diplomatic incident with the Aldmeri Dominion.
The Pariahs
You would then have the opportunity to join the Forsworn and to help them to retake the Great Reach. That is, the Reach in Skyrim, and the http://www.uesp.net/wiki/Lore:Western_Reach in High Rock. As you do so, you'd discover that the Reachmen broke an oath, a long time ago, which bound them to Druagaa and Kyne. You would be offered the choice to restore the oath by binding briarhearts to Spriggans rather than Hagravens.
If you do, you might seek allegiance with the Orcs, who follow the http://www.uesp.net/wiki/Lore:Malacath, and the allied Orcs and Reachmen would retake both the Great Reach and Orsinium. This would allow to learn more about the http://www.uesp.net/wiki/Lore:Goblin-ken, and its relation to Malacath. Maybe the player could visit the Ashpit and learn more about Malacath/Mauloch/Trinimac. The player could also visit the Northern Velothi Mountains, and meet http://www.uesp.net/wiki/Morrowind:Interview_with_a_Dark_Elf There, you'd be allowed to learn more about http://www.uesp.net/wiki/Lore:36_Lessons_of_Vivec,_Sermon_9.
You would also see the Orichalc Tower, and learn more about http://www.uesp.net/wiki/Lore:Diagna#Diagna and about the reasons why the Orcs use orichalcum to make their armors.
You also learn that the first Forsworn Briarheart to be forged by a Hagraven was forged in the http://www.uesp.net/wiki/Lore:Crypt_of_Hearts.
Chim-el Adabal
In the Crypt of Hearts, you learn that http://www.uesp.net/wiki/Lore:Shadow_Magic was performed on Hjalti so that he could become Talos. You also learn much about the previous http://www.uesp.net/wiki/Lore:Shezarrine. You learn that a gem like the one sought by the Necromancers once existed. It was the famed Chim-el Adabal, able to host the souls of Dragons and Dragonborns. And it was used to replace the heart of the first Briarheart... who was http://www.uesp.net/wiki/Lore:Pelinal_Whitestrake.
The gem itself was stolen by the Ayleids to the http://www.uesp.net/wiki/Lore:The_Adabal-a, the first humans to live in Skyrim, builders of the Skyforge and the Lunar Forge. The true, Lorkhanic power of the Lunar Forge is revealed : here the http://www.uesp.net/wiki/Lore:Chim-el_Adabal can be reforged.
You then have to visit the Ayleid ruins of http://www.uesp.net/wiki/Lore:The_Song_of_Pelinal,_v_4, somewhere in the Falkreath Hold, to uncover more about the way Ayleids used the Gem. The Ayleid city, magically concealed, hosts a tribe of intelligent Minotaurs, the descendants of http://www.uesp.net/wiki/Lore:Morihaus#Morihaus and of http://www.uesp.net/wiki/Lore:Alessia and the heirs of Belharza the Man-Bull, as well as some Ayleids belonging to tribes which sided with the Alessian Rebellion. They keep the Chim-el Adabal, which was returned to them by Alessia herself, but empty of souls and broken after http://www.uesp.net/wiki/Lore:Martin_Septim#Martin_Septim used it to repel Dagon.
After you recovered and reforged the Gem, you can use it to capture Dragon Souls, and you have to use it to defeat the Necromancers' leader, who is no less than http://www.uesp.net/wiki/Lore:Wulfharth. You have to defeat him, but before he dies, he reveals that in case you don't forge a new Pelinal, the Thalmor will win.
Meeting the Wanderer
You then decide to seek help in Heldon, to find out how to forge a new Pelinal. One of the Ayleids in Heldon of the concealed town reveals you that some Ayleids sided with Alessia. Some of the Ayleid Tribes refused the perverted, despicable urban lifestyle of the Ayleid oppressors and wanted to stay closer to nature and follow the Old Ways. He now fears that the Thalmor would seek to resurrect the jungle-shaped corrupted Ayleidoon by reshaping the Time and unmaking the victory of Alessia. He doesn't want the Mer to walk into depravation again. He says that Mara visited him during his sleep and showed him a wolf in a Reachmen Temple, and told him that only the lost wanderer could prevent the Old Ways to be broken and the Great Imbalance to blight Nirn.
You then have talk to an old Reachman priest in the chapel of the new capital of the Reach, and he reveals you that the Wanderer is the http://www.flickr.com/photos/47857688@N08/6877590793/in/set-72157629321466509 among the Old Gods. One who came after Ysgramor's Nedes arrived to Skyrim. A man who became a God by the will of Ebonarm, and took the form of a wolf. His name is http://www.uesp.net/wiki/Lore:Sai, and he is responsible for the downfall of the Falmers. He gives you clues leading to an isolated grove inhabitted by Spriggans. There you find a wounded wolf and have to heal it. The wolf then talks to you and says he's Grellan, old companion of Sai. He tells you that he'll lead you to Sai's last descendant. As you follow Grellan, he leads you to the ancient Falmer Chantry of Trinimac, which is located in the http://www.uesp.net/wiki/Lore:Glacier_Crawl, somewhere in the Reach.
There, you meet a Falmer, who tells you he was waiting for you. He brings you to the heart of a Falmer city built around Nym's Airship. There, you meet Sai in person, who tells you that he first thing he did to restore the balance after having provoked the downfall of Falmers was to bring a frightened wandering group of Falmers to this chantry, where they built a concealed city. He also says that the Thalmor, which hates him for being a Man turned into a God, tried to wipe out his influence on Nirn by killing all his descendants. He was authorized by Mara to visit his offspring earlier in the year than usual, which allowed him to save his last descendant, whom he brought there, where his wandering begun. He leads you to Nym's airship, which was freed from its jail of ice, where his descendant, a young silver-haired Reachman, has been welcomed by a crew of Falmer sailors and http://www.uesp.net/wiki/Lore:Star_Teeth hunters.
In the Chantry, Sai's descendant is visited by seven other Old Gods. Together with Sai, they take the Star Teeth collected by the Falmer sailors and turn them into the http://www.uesp.net/wiki/Oblivion:Crusader%27s_Relics#Crusader.27s_Relics, a special gift for the youg Reachman. Then Sai smiles at you, and gives you a special gift, a Lucky Token. "This will provide you some of the luck you will need, my yet-to-be-born brethren in godhood. http://www.uesp.net/wiki/Morrowind:A_Lucky_Coin. Now my blessing is on you, and my wolves fellows won't attack you anymore unless you harm them. My wandering has to start over again. I think I'll spend some time with the Pariah. Those who are deprived of any citizenship. Imgas, Centaurs, Spriggans, Nymphs, Giants, Kothringis, Goblins... Maybe even Dreughs... I don't know yet where the Ways I follow will bring me. " And he walks away, turn into a wolf, and vanishes.
The Lost Heart
You then have to perform the briarheart ritual on the young silver-haired Reachman in the Crypt of Hearts, but you replace his heart by the Chim-el Adabal. When you say him he will now wield the name of Pelinal, he smiles, and tells you that when he tried to defend his mother, by wielding his father's broken sword, the Thalmor Justiciars laughed at him, ironically calling him "glorious knight", before hitting him on the face with a spell who left him nearly dead - which would actually have killed him, had Sai not intervened. "Now, he says, I will wield their nickname with pride."
Stormcrown
You then have to bring the new Pelinal at Heldon, where the Morihaus is summoned by the Minotaurs. Morihaus recognizes the new Pelinal as the real Pelinal, and reveals that you have to bring him where the time can flow backwards. Pelinal then accompanies you to http://www.uesp.net/wiki/Lore:Bromjunaar. There, a tough fight oppose you to the Thalmor, who summon http://www.uesp.net/wiki/Skyrim:Konahrik.
After you defeat them, you meet http://www.uesp.net/wiki/Lore:Shalidor#Shalidor, who still lives in the ruins of Bromjunaar by concealing himself. He tells you to give Pelinal the http://www.uesp.net/wiki/Skyrim:Wooden_Mask, and he sends him back in the First Era. He then brings you to the Four Skulls Lookout, summons a storm, and as lightning strikes you, you are offered the Stormcrown of Talos, as well as the Shout allowing you to rebuild Winterhold.
Congratulations, you're now Dovahkiin, Stormcrown, Orichalc Blade of the Pariah, Benefactor of Winterhold, King of the Reach, Slayer and Forger of the Shezarrine, Dragon Breaker, Mantler of Talos.
So... What do you think about those two ideas ? Aren't they too heretic, lore-wise?