I would love to see Akavir made into a game. Benig a different continent with different customs, its purported link to dragons, and its eastern cultural influence, it may just be a fresh breath of air for the Elder Scrolls series. Not that Morrowind and Skyrim weren't totally awesome, but the setting is starting to become mightily self-contained. More and more subtle retcons, especially in in-game books, suggest that the setting has gone through quite a few tweaks. An entirely new land mass would not be a bad idea.
And Elsweyr and Black Marsh I think won't wory too well as singular game focus. Khajiiti and Argonians are awesome, but their awesomeness comes in part from them being relatively rare. It'll be weird to see them everywhere. But that is just my preliminary opinion.