If Nikon were to actually go ahead and make this, the real sticking point would be price. There's a pretty good chance that this is patent for its own sake, so that no one else can make one, but if Nikon decides this is a product they want to create, how much would it go for? And what would users be willing to pay for it? Digital medium format backs cost tens of thousands of dollars, but I somehow doubt that a digital back for more than $1,000 would go over very well. Could a slightly lower resolution full frame sensor be assembled on the cheap? If they could create one for around $500, good luck finding old Nikons on pawn shop shelves anymore.