If they will make it all of Tamriel then the development time would take 7-16 years, maybe the game with the longest development time, maybe they should wait until more advanced hardware is there. I'd say Black Marsh, it will be a nice setting, Argonains and swamps, and i wish to see Dinosaur-like creatures there, green forests and jungles too will make it the best setting yet, imagine this:
You, with your character, fighting a pack of strange raptor-like creatures in the middle of a tropical jungle, or:
you were in a swamp, suddenly strange a strange creature rise from the middle of the swamp.