I don't want 48 or 56 (or whatever) megapixels crammed into this little sensor. (You want medium format, get medium format.) Having 30 to 36 MPs would be fine, and would add sufficient resolution for serious landscape/still photographers while serving wildlife/sports shooters. There isn't an abundance of current lenses that would deliver results for 48 mps. Wait until the NEXT update in a couple of years before going overboard with a jillion tiny photosites and see how sensors and lenses evolve.
Well, the D5200/D7100 (2 APS cameras) have 2 stops more measured DR than the 5DIII (an FX camera) with a slightly higher resolution. Most Canon shooters seem to think that the 5DIII has enough DR for practical applications (or they are all lying to us which seems unlikely
Assuming that Nikon is simply able to retain the same sensor characteristics when making it larger (which seems a very conservative view considering that the D4x would be coming 1.5 years later at 10+ times the cost), then you would have a 54mp camera with 2 stops more DR than the 5DIII.
I don't see any problem with that really.
Lens wise, there are many options that are not really challenging the 36mp sensor of the D800: Nikon 24mm f1.4, 85mm f1.8 and f1.4, 45mm T/S, 85mm T/S, Nikon 70-200 f4, Nikon 70-200 f2.8, all the big guns even wide open, Sigma 35mm f1.4, Zeiss 25mm f2, Zeiss 50mm f2, Zeiss 100mm f2, Zeiss 135mm f2, Leica 180mm f2.8,...
And those are only the top performers I can think of now, many other lenses are performing very well in real world applications.
One thing that is not always well understood is that a higher resolution camera will still deliver a better image with an average lens than a lower megapixel camera.