So, you all do realize we have a new thread about this almost daily right?
When I saw another one of these I wanted to bang my head into the wall. But the last one was locked, so w/e.
While Skyrim is what I'm preparing for as TES V's main gameworld, I would like an expansion(assuming Bethesda changes their mind about not making expansions, because I thought that was a ridiculous decision) that takes place only in the Imperial City and on the surrounding land which makes up the Imperial City Isle, but in more detail. Shivering Isles was approximately 4 square miles large. If Bethesda could do that for the Imperial City Isle alone, I believe they could show us the capital of Tamriel in a more detailed and believable way.
I for one hope that when Umbriel uses White Gold Tower to break free from Oblivion, in lands right on top of the Imperial City and completely destroys it. I hope that happens for a few reasons, namely so that the Empire crumbles completely, and so that if they ever set a game in Cyrodiil again, we'll have something new to see.
To be the wild card again, there where rumors that "Yokuda" has resurfaced.
Seeing a previously inhibited, then destroyed and now recolonized island would be neat, especially since we could see what developed on there in the time it was sunk. Maybe a new species evolved on it. Actually it could make for a great conflict, a new race that has taken residence on Yokuda, the descendants of the previous inhabitants demanding the land of their ancestors and colonists wanting to claim the new land as their own.
Yokuda never sank completely. The large majority of the continent sank, but there's still a lot of it left. You're probably thinking of Thras, which was sunk completely, but then resurfaced later.
Personally I hope they set the almost-definitely-coming MMO on Yokuda. We know next to nothing about what it is like nowadays so it's essentially a blank slate.