depending on the price, it will just be a poorman's medium-format !
and who needs to shoot 75MP images by the way ? which lens will be good enough for such a sensor ?
even with the D800 @ 36 MP the lenses recommended by nikon are maybe less than a dozen so far.
it makes no sense to me, they should launch a new 72mm format if they really want to make things properly, and of course bigger and heavier lenses ! otherwise it will be a bottleneck to stick with actual full frame lenses.
besides, most of the problems these lenses have are because they're too small and too light.