I would dispute the certainty of a PSThree, on the grounds that it has largely been the business of the market leader to do such things (NES, SNES, PS1, PS2). Sony just happened to be 2 for 2 up until this cycle. I'm not counting the Panasonic Q because of a limited run in only Japan.
If the market momentum is lacking, it would be better to prep for an early PS4 launch instead.
The only way I see a PSThree is if they decide to skip the next generation and do a relaunch/mid-cycle launch, which would also be unprecedented, since only the market leader has ever wanted to extend the previous cycle.