I would love Vice City to make a return in the next GTA, as would many others who believe it will happen. Here's the problem with it though. This idea came to mind after GTA IV was revealed to take place in Liberty City, implying the potential for the next trilogy to all be set in remakes of previous settings. The problem part: Rockstar is full of surprises, it's never easy to tell what they will do. What we have to hope for is that R* won't recognize that the community is highly speculating VC for the next setting and say "Oh well we want to shock them so let's make it something else!"
Realistically, I don't think they would do that, they've more than likely had the next GTA planned way ahead of time before even GTA IV was released, so there's no way that we could change those plans at this point in time.