With the trend of ES series I think it will be set in Hmmerfell. However, after looking at the geography and creatures that inhabit the black marshes, I would really love to see a game set there.
Swamp land with huge laviathans and paranhas, swarms of bitebugs, huge prehistoric inspired birds with saw like beaks! The cities are also more sophisticated and imperial influenced than I expected.
Tribes of primative argonians inhabit the thick marshes and deep reaches of the imposing Murkwood forest.
Dunno about you guys, but it sounds really interesting. A place where men & mer are the outsiders, where the guerilla tactics and waterbreathing techniques of native argonians can spring traps on unsuspecting travellers, and if the lizard people dont get ya, the native fauna certainly will!