Asia was already done in GR2
east europe was done in GR1, as was africa and cuba(which is kind of like southern asia in terms of terrain and such)
GR3 is in mexico city.
This leaves Austrailia, Western Europe, America and Canada
since this game is kind of based on alternate futures dont know if the middle east would be an appropriate choice given whats going on now and what would be goin on in about 7 years.
if the urban combat is very good in GRAW maybe they should try to do more urban stuff. Rural and suburban maps might be cool. "enemies spotted at the mcdonalds, they have minivan support!"