I think we'll be reaching a graphical plateau soon. Once Photorealism is reached, where do you go from there? The graphics (and the processing power to support it) are what's driving up the costs of today's consoles. Once the plateau of Photorealism is reached, that cost aspect of consoles will decrease in expense and they'll have to do other things to warrant a reason to release new hardware (similar to what Nintendo has started with Wii).