I'm guessing a worldwide summer release is on the cards. Sony still has plenty of time to announce a lineup for Q4 to go along with The Last Guardian, Agent, Twisted Metal, Resistance 3, etc. However Sony doesn't have much longer to announce a major release for the summer period that they typically have.
2007: Warhawk
2008: Metal Gear Solid 4: Guns of the Patriots
2009: InFamous
2010: ???
Honestly, I'd say that the summer would be an excellent time for GT5 to release. It will create a MGS4 sized spike for summer PS3 sales and GT5 is a series that sells largely on legs. The sooner it comes out, the more it will sell. It would also tie in with the launch of 3D capable televisions from Sony.