Southern Morrowind (not Vvardenfell) and north-western Black Marsh.
The geographical, cultural and political situation there is very interesting, especially after The Infernal City. I'd imagine the Empire, since peaceful ways are unlikely to work, would start an invasion against Black Marsh sooner or later, struggling to secure more than the West, but not really needing much more than a larger outpost to see what's going on in the Province, since Argonia is not very interesting for the Empire and they'd only need a town or two there to claim the country theirs.
The player would probably start out there, there'd be an unconventional warfare-like atmosphere at the "border" to the "wild" Marsh, and deeper within the country the player would meet exotic creatures, culture, vegetation etc. That place would be very dangerous, but the hero would try to bring peace to the region. The main quest might then lead the player up north, at first to the very southern Morrowind, partly controlled by what remains of the Argonian population there after the Umbriel incident. Going north, things become even worse, and Dunmer daedra-cultists would be everywhere - however, those would not be "bad guys", but the player would instead learn about the culture of those Dunmer who came back to Morrowind, and the main quest could resolve around bringing peace to the region around Cyrodiil, Marsh and Morrowind and uniting these areas under the Empire.
Especially Morrowind would be interesting, since alot has changed, and the Dunmer who might eventually re-populate it would be alot more mysterious and alien than they already were, since they live in a damn unfriendly environment and want to stay away from the Empire and the Argonians. The Argonians would be split in two parties, the An-Xileel and the now very rare empire-friendly Argonians... (Depending on what happens in the second book, the situation will probably look much different, but interesting nonetheless)
I just think the area there has alot of potential for a fantastic setting, not unlike Morrowind, and for politics and stuff.
in this i disagree i think the provences should be split up in the new games with the player creating the nations and then they create a new game where after a lot of adventuring and quests you become a general and try to captur the other provences to create a new empire under any one of the nations because it would be like 30 years from now with a gigantic well done game with all the provences