I personally think that they are going to return to Vice City in this one. The original GTA trilogy (GTA 3, VC, and SA) took place in Liberty, Vice City and San Andreas and in GTA 4 they began a whole new chapter. I think that they will make this one a trilogy and the next two games will take place in Vice City and San Andreas.
Also, what do you want the main character to be like? I would personally prefer playing as either an Asian character (TRIADS!!!) or play as an Italian character and do the whole Mafia thing, that would be pretty sick. Any ideas folks?