In the next Elder Scrolls game, I hope to see more joinable factions. I mean, I want to be able to join not just the Mages Guild, the Thieves Guild, the Warriors Guild, The Dark Brotherhood, The Imperial Legion and (possibly) the Rebels, but also factions like the Vigilants of Stendarr, different clans, Vampire clans, packs of Werewolves, and also Daedric Gods-worshipping factions. I want to be able to join every named group in the world, and It would be really nice if it would work like in Morrowind: that if you joined one faction, another one would be mad at you, and vice versa. That's all.
Something I'd like to add on about role-playing and guilds and using Radiant Story in future Elder Scrolls:
The Stormcloaks vs. Imperials decision was actually fairly well-done (although it would be nice if their quests were more open-ended), as you can see plenty of threads where people are genuinely split on which side they support. In doing so, they actually do a better job than BioWare often does, where the decisions have obvious black-and-white morality contexts. I never really could be this indecisive and take so long to weigh my options in most BioWare games, and because of that, this would be something that BioWare could learn from Bethesda.
... However, this is pretty much the only such choice in the entire game. So much of the rest of the game is so shallow in its quests and so restraining in what it allows you to do with your character, other than roam freely and kill everything in sight, that it really begs for more of these one-faction-or-the-other choices. Whether or not I choose to join the mage's guild is no real choice for a character who is a mage. It's not a choice that expresses any values or beliefs or my reasoning of what moral failures on the part of one faction are justified, and which faction's moral failures are inexcusable, it's just somewhere you go because you're a mage.
In Morrowind, Oblivion, and Skyrim, the fighter's guild is directly opposed by some other guild. In Morrowind, you couldn't be a thieves' guild member and be in the fighter's guild. You had to choose. Why can't you choose to join the Silver Hand instead of the Companions, or that Blackwood something or other (unfortunately drawing a blank on the name) instead of the fighter's guild in Oblivion? That would give players the ability to evaluate which guild they actually preferred. Joining a fighter's guild when you are a fighter is not any real meaningful choice, but telling the player they have to pick one or the other of two opposing fighters guilds makes players have to stop and evaluate who actually better serves their own RP interests.
Further, that wasn't really part of the point I was making - I don't really like these "guild" factions becoming the only real factions with quest lines that exist in the game, because "being a mage" says very little about your character's actual beliefs or choices. The fact that you don't even have to be a mage to join the mage's guild makes it even worse. There's no reason not to just sign up for all the guilds and get everything. By making factions that actually stand for something other than what skills you have points in, but some philosophical outlook, you introduce some of that delicious gray on gray moral decision making.
Honestly, the shortness of the guild quests would actually not be such a problem if you did one simple thing - make the player do some Radiant Story quests as "grunt work" once they are entry-level associates of a guild to "earn their place" in the guild.
If you just work on making the dynamic quests interesting, you don't need to have plot quests except as capstones or dramatic turns in the plotlines of faction or main quest lines. I would like to say, however, that means you
really need to work on making procedurally constructed quests interesting and varied. **
For an example, Mount and Blade has essentially no plot at all, just 6 warring factions and a bunch of random quests which are set to repeatedly be offered to the player. It doesn't suffer for lack of a plot, and in fact, just helps to free up the player from any sense that they have some sort of railroaded main plot forcing their character to be anything other than what the player wants him/her to be.
Work on making an immersive world, and making quests where if the local gnoll encampment goes too long without being exterminated, they will start raiding Farmer Bob's outlying fields, and Farmer Bob will then put in a request for the local hired blade faction that has had a good success recently to get rid of them, and you have a good quest set up. Better, the local economy could be harmed in-game until the gnolls are gone, while it improves the safer the community is, making those random quests actually give you the feeling that your actions have a concrete impact upon the world.
Then, you can make which faction of "local hired blades" the farmer goes to become based upon the publicity of various rival "fighter's guilds" that the player could join. Picking one of opposing fighters guilds that are all basically mercenaries, but where the mercenary band you join with might have radically different philosophies as the other fighter guilds, and different clients that prefer to go to them (so long as their reputation hasn't been destroyed by the competition), and you have a way to keep factions and guilds interesting without having to go through hand-painting and voice-acting big dramatic "ONLY YOU CAN SAVE THE WORLD" plotlines every 5 seconds.
Give players the ability to hire immigrating procedurally generated NPCs that are looking for work to join their guilds to replace any losses, and a much better follower control system, and you can even have quests where you take out guild members to fight with you and die, but not require reloading or having a permanent hole in their company roster.
Spend the time to make procedural gameplay/Radiant Story a serious core mechanic of the game, and it can outright carry quite a bit of the heavy lifting of making a detailed gameworld for you, Bethesda. Just look at Dwarf Fortress, a game whose procedural world generation builds a continent with a 1000 year history at the push of a button, and whose creator is currently working on making a truly dynamic living world with a population of hundreds of thousands and a working economy.
Any company can make a "save the world" quest, but Bethesda is known for creating a jaw-dropping world with incredible verisimilitude, and working on improving these aspects of the game helps to make your games more truly unique.
----------------
** EDIT: Interesting and varied quests means quests that aren't just go-here, kill that. It should be something that actually relates to the state of the world around the player, so that maybe if crime has become a big problem, you start getting requests to catch thieves or guard important goods. Alternately, if you are part of a criminal faction, the marks should adapt their defenses to guard against the types of crimes you commit. Again, invisibility spells breeds guards using scent dogs to catch you. Going in brute force? They might hire some powerful mages or warriors to stop you.
Likewise, while I like the quick travel option in this game, you might make an Indiana Jones style red line going across the map (especially if the game is going to have to pause to load the region, anyway,) and have random encounters when you try to fast-travel stop you mid-travel, rather than simply appear when you show up at the city gates.
That way, you can also take on jobs as a caravan guard, and have random encounters where you protect the caravan without making the quest take a huge amount of time just walking alongside the caravan. Also, make some diversionary wolf pack tactics occasionally on hitting those caravans, as well - small threat hits and runs to lure the player away while the main force strikes from the other side. Something to keep every quest of the same type from feeling the same. That's what procedural coding is good for - making things a little random.