In my mind, only the GFX card is up for discussion. Ivy Bridge and USB 3 are givens. I think everyone agrees on those two items.
I may be in the minority, but I do not think we'll see a retina display on desktop models. I don't see ANY benefit for large screens (esp. 27"+). The 4K screens are simply too expensive at the iMac price point. Touch screens for desktops....Would not want it, would not buy it.