When we judge sharpness of a digital image, we immediately go to 100% and see what an image looks like. I can with absolute certainty, that a large number of shooters who think they have great glass and shooting technique will not have a great experience. The D800/D800e demands the most of both glass and shooter to get a 'sharp' image, so to go to a higher resolution without having answers, you're asking for upset customers. This is the reason I think there is rumors around a Canon MF - that to push the resolution that high, and to put a 20 year old EF lens in front of it, it's most likely going to suck. Element slightly out of alignment - it's going to show.
I love MF - Phase One certified, and have a H4D-50. I would prefer that Canon do a retro styled high megapixel / high DR fixed lens as a starter, since they can control all pieces in one package - ala x100s. Once they can show the world how amazing it looks they can put the same sensor into a DSLR, be it 35mm or MF.