No retina display please.. No graphic card out there can drive that amount of pixels sub-30fps, yet..
Actually there could be. Too many folks are making the false assumption that Retina would mean doubling the highest current res but the math doesn't play out to that. Under Apple's own published math you only need about 12% more pixels on a 27 inch and 15-17% more on a 21 inch (which they aren't likely to do since that is the more consumer model and folks won't pay the higher price).
So they might not need some super crazy GPU to push that amount. Or if they decide they want to increase the power they might go with a 'desktop' GPU rather than a mobile one, have sorted out a way to put in a second (they would have room if they kill the internal ODD) etc.
I'm more curious what they might do with making a larger Cinema Display model and even perhaps one with the power and frame rates to handle even 3d material cleanly. I'd take a 40 inch Retina 3d capable Cinema Display as a tv any day. With both thunderbolt and HDMI I could hook my computer and blu-ray to it as well as my Apple TV and be very happy.