Non retrofocus wide angles are problematic with digital sensors, because the large chief ray angle. It is possible to build truly great retrofocus ultrawides as shown in this topic: http://www.luminous-landscape.com/forum/index.php?topic=75282.0
I don't really think that there is as much business opportunity for Nikon in designing a very limited MF camera as there are several cameras to fit the bill already like the Hartblei H-Cam and Alpa FPS.
Thinking about Nikon/Canon and
deep wider throats, I wonder if Nikon might feel this a good time to produce an alternative to the 135 slr bodies and try out a variation on the Merrill idea: a specially designed body, with live view, that could accept a couple of PC/Tilt lenses to new design, even work off a larger sensor. It would have to be expensive, but specialist stuff always is.
It would not compete with their normal product line any more than did the 38mm lens in the dedicated Hasselblad of yesteryear, supposely the best lens of its era in that focal length, damage Hassy. Wouldn't even need a reflex box to screw up design parameters: a tripod would be taken for granted.