If you look in the instruction manual for Gay Tony, there is a little section in the end that talks about Vice City. It's like an airport ad that says "Next stop... Vice City".
It makes sense that it would be Vice, since it is the same cycle they did with the 3 series.
They have established cities already that they want to redo before going to a new city, that was part of the big draw to GTA IV, a redone Liberty City.
Part of the big draw to GTA V will be a redone Vice City.