Speaking of new games being new provinces, that's lots of years in the future, and with advancing technology and equipment, more time even than it took to make skyrim. And that might even double if they ever hope to please the fanbase by making a new game multiple times better than the previous.
I wouldn't mind if it were the mainland of Morrowind, you only really were on Vvardenfall in TES:III
So the mainland IS a possibility for DLC, in my opinion.
EDIT: Also reading up, only Vvardenfell was destroyed by the volcano. The mainland isn't damaged as far as I can understand.
High rock is also relatively small compared to other provinces, so it would be a nice DLC as opposed to a whole new game for being such a small province.
EDITEDIT: I take that back about High Rock, southern provinces are small too.
TripleEdit: Plus, if we run out of provinces for games (From wiki):
Other lands are known to exist, though they have never been seen in games. They include:
Akavir, an often hostile continent to the east of Tamriel.
Aldmeris, a fabled continent from which the Aldmer came to Tamriel.
Atmora, a frigid continent to the north, home to the ancestors of the Nords.
Cathnoquey, a region of land that lies between Tamriel and Akavir.
Esroniet, a small island kingdom that lies between Tamriel and Akavir.
Pyandonea, a continent to the far southwest of Tamriel, home to the Maormer.
Roscrea, a region of land that lies between Tamriel and Atmora.
Thras, an archipelago to the southwest of Tamriel, home of the Sload.
Yneslea, a region of land that lies between Tamriel and Akavir.
Yokuda, a ruined collection of islands blasted by a cataclysm to the west of Tamriel, original home of the Redguards.
lovingQUADEDIT: Especially Akavir, since Dragons came from there... But I haven't finished the main questline, so I don't know what happens actually.
Poll