If we might speculate about the next installment, only thing we know for sure is that it will be singleplayer. As for province of Tamriel where it will take place, well:
Arena featured many regions from all Tamriel, as far as I know;
Daggerfall had parts of two provinces (High Rock and Hammerfell);
Morrowind had part of a province (Vvardenfell);
Oblivion has one province once again (Cyrodiil);
If I were Bethesda

I'd continue this list with making a game with two or more nearby provinces (not in parts, but in whole). Say, Elsweyr and Valenwood, or High Rock and Skyrim and Hammerfel. Might even be that one province will be added in some kind of expansion for Oblivion. Why not?