No. Forza is stealing too much thunder from GT, and racing games in general seem to be on a downturn since last generation.
It remains to be seen whether Halo truly gets its thunder stolen by Call of Duty or not, but if the pre-order chart is anything to go off the answer is probably 'no'. The games seem to be able to live separately by being different enough in style that people are inclined to buy both.
I don't expect we'll see GT6 for the PS3 though. GT5 is pretty much just a money-printing machine for them at the moment with still a fair amount to offer, and GT6 is probably too important for getting PS3 out of the gate. Or Vita off the ground.







