I kind of wish they would do a new location other than what they have made in the past.
I think this might be the last time Rockstar reboots the series, or completely redesigns the cities. They've been remade since GTA I. I think a while back I remember seeing Dan Houser in an interview state that IV's Liberty City is the way they always imagined it, and that they're happy with what they turned it into as a modern take/satire of New York.
After they most likely redo Las Venturas, San Fierro, and Vice City, I can totally see them finally moving onto some new cities - or making that one GTA game that Leslie Benzies dreams about, where it contains all (LC, SA, VC) the maps in one game.