When we talk about the customize GPU, its basically optimized gaming solution which I think will have all the juices required for next gen games. Especially if it supports latest version of opengl APIs + proprietary solutions.. edram will make alot of difference.
I think what makes difference in next gen will be the exclusive content and from processing/memory perspective more on AI, complex environment and stuff like that. graphically it may be somehow similar but not notable difference between all platforms.
WiiU, if launch earlier and got enough userbase which may be the base platforms for companies to work on and especially when Nintendo is more open to make more partnerships with 3rd parties, it will be interesting to see what comes out of the doors..
The only way PS4/Xbox3 could get enormous leap from WiiU if they get magic wind to make the gpu small and cool enough which we all know is not possible at current level. Else we may get many heating issues after launching. And there will another loop of losing tremendous amount of money by them by selling system lower price.. gosh.. they really love gamers than their businesses
The way expectations are going, I think people will be disappointed with Sony and Microsoft rather than Nintendo