I say let Bethesda keep the east coast, and let Obsidian have the west.
Revisiting some classic Fallout 1/2/Tactics/Brotherhood of Steel (yes, I went there)/Van Buren locations would be much more appropriate, IMO.
Granted I through in the native american because im a little sore my people were supposedly or appear to have been wiped out. Thanks bethesda. Real nice.
It's not like Bethesda made the previous four released Fallout games. :\
Also, you might want to check out the http://fallout.wikia.com/wiki/Blackfoot tribe, who happen to be mentioned in New Vegas. They're part of the Legion now.
...During this time several wandering groups of Native Americans (who left their reservations after the American government collapsed and there was no longer anything to stop them from claiming nearby land) established a relationship with the raiders/ranchers and the two groups joined together for greater strength; the tribes gain access to some technology and a fortified home, while the raiders/ranchers gained access to skilled outdoorsmen who knew the area very well.