Not impossible.
GTA V is last game in series for current gen consoles. Previous one was released four years ago.
Rockstar North is a huge studio, there's hundreds of people working on GTA games.
In the meantime they produced Red Dead Redemption and Max Payne 3 (El Noire was developed by Team Bondi).
Engine is the updated version of RAGE, which is already well optimized for PC (Max Payne 3), looks ten times better than in GTA IV and they probably prepared assets for the game during last four years.
I really wouldn't be surprised if console premiere of GTA V is this Christmas season. PC version probably on march 2013.