My musing was a digital camera that works like a film camera. Frank's original idea of the FM-D is what I'm also thinking, and having the features that David described. Nikon calls the NEF image file a "digital negative." So...the idea would be a FX camera that looks and feels like a FM. I'd be okay with an LCD screen, the controls would be basic, like a film camera.
The idea would be to "develop" the "digital negative" or NEF file on the image editing program of your choice, and although it would be nice if Nikon had such a program, it would not be a requirement. The idea of a Nikon program for image editing would be nice if you like Nikon's Picture Control settings, otherwise any editor should do.
As David said...won't ever happen, but I think it would be fun. It would be a "niche" camera, and if you need more robust features like shooting JPEGS, then there are already plenty of choices available.
: )