I already have a quest mod planned for TES 5 if I like the game. I would've done it for Oblivion if http://www.gamesas.com/bgsforums/index.php?showtopic=1051034 didn't end up getting as huge as it did, by now I have no interest in starting another large quest project.
Basically for a seamingly innocent quest the player is required to join a trading ship on it's way to [insert nearby province here] to keep an eye on things, because there has been a thief on board in the past. Before he enters the ship he leaves all of his possessions behind and is given clothes to not look out of place. The player gets to do a little investigating, and after giving his opinion to the captain he retreats to his cabin.
Not much later the player wakes up. The ship has hit a storm and is sinking. After getting out of his cabin (the door will be blocked so it'll have to be forced open) he needs to get out. Outside, in the middle of nowhere, the player hangs onto whatever sturdy looking floating piece of wood he can find and passes out.
When he wakes up he finds himself in a sea cave like http://ramblingsdc.net/OldPhotos/LookingOutCaveSmall.jpg, washed up with pieces of the wreckage on the shore. There'll be a young man on another piece of floating wreckage, presumably dead. When the player goes to check he finds out that he is in fact still alive. The player needs to manually drag him to the shore (inside the cavern).
The guy wakes up, has a conversation with the player and becomes a companion.
When the player and 'the guy' make their way through the cave they find a small village, with people surprised at the arrival of their new guests.
The inhabitants of the island are people who previously got caught in a storm and ended up on the island as well, 20 or so years ago. They were never rescued and for reasons currently unknown they have not been able to leave the island.
The player will have to work together with his companion to find their way off the island. Through dialogue choices the player can influence what his companion thinks about him, positively or negatively. How the companion has been treated during the story will play a vital role in some of the crucial later parts of the story. Because the player and his companion have no equipment at all, a few of the first quests will deal with gathering some.
Along with the main story of the island there are side quests that can be completed for people in the village.
The rest I haven't worked out entirely yet. Basically there's another group of people living on the island, researching it with 'evil' intentions.
Now here's where I'm bending the lore a little bit, and things get rather complicated (especially for me to create). With an amulet this other group is developing and special locations on the island the user of the amulet is able to travel through time: 10 years in the past, or 10 years in the future. Time only changes on the island. One thing I'd like to be important is the presence of choices and consequences in the quests. By allowing the player to go 10 years in the future it'll be possible to show the longterm consequences of his actions. Of course the area that the player can explore in the future and the past are a bit more limited than the present, because recreating everything twice would be a lot of work. But I'm not the greatest landscape designer and this is going to be a solo project so the island isn't going to be huge anyway.
Then there'll be an occassion where the player is able to go back to a specific time to correct his own mistakes, etc.
It's probably obvious by now that my influences are Chrono Trigger and Prince of Persia. And a theatre play I saw. And no, not the season of the TV series Lost where time travel comes up. I came up with the whole concept before that season appeared here.
The WIP name would be Akatosh Island, because Akatosh is considered the god of time.
There's no guarantee that I'm actually starting a quest project for TES V but if I am starting something it'll most likely be this.
edit: I've actually never written any of this down. I'd better copy this post.