I'm guessing it will most likely come out at the end of next year.
Because the last of us is being released in may, and Sony doesn't have any huge games planned for the fall. Usually (like with the last of us) they show off their next biggest game at least a year before it's release. (uncharted 3 was shown off at the VGAs pretty much a full year before it was released as well)
So I wouldn't be surprised if Sony releases the PS4 during the holiday season.
Solid theory, like it --- "There are TONS of games that look BEAUTIFUL. It's not a matter of polygons anymore, it's a matter of ART DIRECTION now" PSN: Monkeyman0111