Rockstar's lineup for fall and winter of this year is...
A new Midnight Club game
MTV Celebrity Deathmatch
Grand Theft Auto 3 (PC)
A new Grand Theft Auto game
That last bit is what makes me think that Grand Theft Auto: Vice City is actual. "Miami" wasn't in the works, but it's mockup probably was.. all the rumors and subsequent denials is very likely to have been a PR trick.