Whenever a sensor is developed with smaller cell sites over a given sensor format, the probable first effect is that (AA filters aside) is that lenses that seemed to be acceptable in the corners just look soft. This is not such a big a deal if the ultimate print size is not increased, but if it is or if you pixel-peep, the additional softness will become annoying. Using Phase as an example, I found that going from a P45+ to a P65+ to an IQ180 at each step put more demands on the lenses. This can be predicted upon careful examination of the MTF plots. Say, for example, that you consider "nice and sharp", a lens that delivers 50% contrast at your pixel pitch times by 2 (to get to line pairs per mm) and if you shoot with a 5.2 micron sensor, that converts to about 96 line pairs per mm.
Looking at the Nikon 35mm f1.4 G lens MTD plot, you can see that at 30 lines per mm and at 21.6 mm off center (the corner of a 24x36 mm frame) you see contrast at about 30%. This lens will begin to appear soft in the corners of even a 15 micron pixel pitch sensor. Of course an AA filter just makes it appear to be a touch soft all-over.
True apparent sharpness is also related to the subject frequencies and the sampling frequencies desired. Nyquist criteria dictate that 2 samples per period is the minimum sample rate to recover a frequency component. However, all that gives you is a square wave or a picket fence with lots of moire. A smoother sample may be possibly in the neighborhood of 4 samples per period which means that your 96 line pairs per mm might really help you get smooth samples of a 48 line pair per mm subject.
At least theoretically, it therefore seems that several of the nikon lenses I have browsed will go unacceptably sharp just in the corners assuming that 50% contrast is your limit.
Comparing those lenses with what I shoot on a technical camera fitted with an IQ180 shows a similar story but for a larger sensor. At F/8 with the Rodenstock 70mm Digeron-W and 40 lines per mm it gets to about 30% at the corners but stays above 50% to about a 35mm image height. There is more contrast at higher frequencies at more displacement from the image center.
So it looks to me that if the cursed AA filter is removed, the better Nikon lenses will approach but not quite equal medium format corner resolution should a 36 MPix FX sensor be produced.
BUT, I have 80MPix in an IQ 180, so for an equivalent finished print size, it will need less scaling so it will appear to produce more sharpness over the final print.
YMMV and of course, these MTF plots are theoretical and actual lenses usually are not quite as good.
OTOH a D800 is a different animal than a technical camera and it is usually held differently. Remember that a smaller cell site also requires a more stable platform or a faster shutter speed to reduce motion blur which often becomes the deciding factor in sharpness for the hand-held shooter.
-bob