There is no way a company could be stupid enough to implement this in the way the OP suggests, because it would piss off every single gaming demographic there is. The lifers would rage hard and bombard Sony with complaints and lead boycotts that might actually work for once, and the casuals would either stop gaming and go find something else to do or just see what's new in Farmville.
If this was used in the same way that a lot of apps do, though (i.e. you can download the full game from PSN with ads then pay to have them removed) then I think it would work pretty well, and I actually see that being Sony's idea since the App Store has been a pretty big damn success.
If this was used in the same way that a lot of apps do, though (i.e. you can download the full game from PSN with ads then pay to have them removed) then I think it would work pretty well, and I actually see that being Sony's idea since the App Store has been a pretty big damn success.