And then there's the Thalmor,too.
Elsweyr, Black Marsh, they're both unique provinces. A game situated in either of them would be great.
If anything, I think Black Marsh is a safe bet. If they happen to want to get back to the "alien" feel of Morrowind the Marsh is supposedly even weirder than Morrowind.
There's also Akavir, a whole new CONTINENT of possibilities. The Nerevarine's supposed to be there now.
I for one don't want wierd. Wierd is easy. Wierd is the reason that -- of all the TES games since Daggerfall -- Morrowind was the only one I didn't finish because I lost interest (although to be honest, the fact that the mobs became ridiculously easy was also a factor).
Going too wierd is bad as far as I'm concerned.
While Daggerfall included Hammerfell and High Rock, It also included, well Daggerfall. Furthermore it was so long ago I doubt very many current TES fans ever played it.