Myeah, Vice City is probably #1 on my wishlist. But! I'm really starting to warm to the idea of something more north-eastern, maybe midwestern. Carcer City might be too depressing, assuming Detroit as the main inspiration. Maybe something like a hybrid of Philadelphia and Baltimore, with a nearby Atlantic City. Or Boston.
Personally, what I think could be cool for Rockstar to do, would be doing one or two more modern-setting games in this continuity/universe, whatever you want to call it, before starting a new line, that's all period-settings, eg. San Fierro or Las Venturas in the 70s, Los Santos or Vice City in the late 70's/early 80's, and Liberty or maybe Carcer in the mid-80s.