Both the cost and the technical specs are cost prohibitive. We may see a screen that supports 1080p next time (probably a WUXGA - 1920x1200), but not anything near the specs of the current retina display. Anything more would be ridiculous on a screen of this size.
My rough calculations would put the retina display for an iPad at about 2660x1774. I know that is quite a bit more than the current 1024x768, but we probably don't need anything with that high of quality for an iPad.
Close but no, since the retina display has double the pixel density than the ipad would too. 2048by1536. Apple would want to keep the 4:3 aspect ratio. Anyways i think that would be pointless and to expensive.