User blog comment:SleepingIII/Elder Scrolls Online - The Road Ahead (December 4th)/@comment-75.144.108.174-20150113162439/@comment-5469467-20150113224325

Hmm... I'm thinking they might be better off doing it province-by-province for now. If one game featured the entirity of Tamriel, more than a few corners would likely have to be cut with each individual province, so each one wouldn't get the same size and level of detail as they would with an entire game dedicated to them.

Even if every province was made as big and fleshed out as they would be in their own game, the game would have a pretty long development time. The filesize also wouldn't be pretty if we're talking a game that could be nine times the size of Skyrim in terms of geography (give or take), to say nothing of assets.

Don't get me wrong; it would be fun if they could get it right. But it simply may not be feasible.