I'll keep it really simple.
PPE in a PCIe configuration, as a stand-alone card, will not fly. You'd have to choose between a single vid card and a PPE card, rather than SLI with a PPE card (or Crossfire with PPE).
I don't see the PPE increasing framerates, but rather increasing realism...which is what they're going for. I mean, c'mon......when you're topping 200FPS in a game, what the heck are you complaining about??
Where I DO see PPE heading is an integration into the video card, which would make the most sense. I can definitely see the allure, in the current format. Let's take me, for example. I don't have an SLI motherboard, nor do I have $500 to spend on a single video card. However, I can drop $200 on a BFG PPE card, pop it into one of the gazillion PCI slots I have available, and make my X800GT look a hell of a lot better............and for less money than an X1900. It's all in the market.
At any rate, I don't see this new development as really aimed at hardcore gamers, but it is a plausible add-in for the other 90% of the computer user world.