I believe that in less than 10 years, Nikon will have a full-frame camera (DSLR, Mirrorless, doesn't matter) for around $500. Moore's law still applies for the time being with computer hardware, unlike the other mechanical parts of the camera.
That means that the industry will be back to the 90's in one important respect. Arguably, the best professional SLR every made was the F5 and it sold for slightly more than $3,000 when first introduced and dropped to around $2,000 just before the F6 came out. The only really important difference today I think, besides all the incremental mechanical improvements, is the digital part and that price is coming down fast. I predict that when the D5 comes out, Nikon will be hard pressed to argue that it is worth more than $4,000.
So if Nikon wants to expand its market and charge a premium price, medium format is an option. We have already been sensitized to paying $6,000 plus for Nikon, Phase One, Hasselbad etc. It would require a new lens lineup with a new format, with 20-30 lenses. However, if the sensor was big enough to offer an obvious and compelling improvement without being too big to fit in a D4 body (60 by 40 or even 60 by 60 perhaps), perhaps there is a market that would be focused on studio photographers (FX is good enough for sports action and news photographers) with a strong prosumer secondary market.
I heard about a Nikon patent for a medium format lens, so I am sure that Nikon has thought about it.
What do you guys think?