OK,so my theory is based on M'aiq.
In Oblivion M'aiq makes fan of Werewolves saying:
Werewolves ? Where ? Wolves ?
Men that are wolves ? Many wolves.
Everywhere. Many men.
That is enough for M'aiq
Then Skyrim comes out,and it have Werewolves.
In Skyrim M'aiq says though:
Werebears ? Where ? Bears ?
Men that are bears ? Many bears.
Everywhere. Many men
That is enough for M'aiq.
That could be a hint that the next game of the series will feature Werebears.
Assuming that M'aiq is the voice of developers and the above facts,one could say that these lines hint that the specific were-creature that M'aiq talks about will be in the next game.
If that's the case,then the next game will be on High Rock,as Werebears are founded only in Skyrim,Morrowind and High Rock according to the Lore,and since Skyrim and Morrowind are already out,that leaves us with High Rock.
Another thing to notice is that High Rock is at the western part of Skyrim.Since Morrowind TES games have moved westward,and if we consider the westward movement to be the way Bethesda wants to release the games,then High Rock would in that case too be the most possible province of Tamriel to be featured on the next game.
It would also be interesting to see how Bretons who are half Elf,half Humans (Nordish) will react to the High Elf-Nord+Imperials rivalry.
So I think that the next game of the series will be: The Elder Scrolls VI: High Rock.