From what I can tell there are a couple of points which excite people about these cameras:
- Interchangeable lenses (except of course for the X100 which almost immediately drew criticism that it was an interchangeable lens camera, to which rumors now abound that Fuji will indeed pursue such a camera).
- Simplified manual controls (Having played with a Leica M9 I have to admit it was sheer joy using the simple dials and buttons of pre-electric cameras. The true irony is that an experienced photographer can work faster with the older controls ala the Nikon F4 and and FM than the newer button frenzied layout of say the D5100).
- Small (Forget pocketable for the time being. Compare a D3 with an FM and you get my meaning. The modern well built camera can be used as a stop for a truck on a hill. It's big, it's heavy).
- Good image quality coupled to RAW image capture.
So, why not create a digital solution for the old manual metal cameras such as the Nikon FM? Nikon has produced the most incredible cult classic in the chassis of the FM. Not only that but the FM spawned a legacy of cameras - the FM, FE, FM2, FE2 and FM3a - that had interchangeable accessories, the back and MD12 motordrive which are the most important in this case.
Why not create a digital back connected to an MD12 chassis that can be attached to any of the FM series cameras, or at the very least the FM2 and up (The FM lacked some of the electrical components of the the later models). The parts are there. I suspect that the buyers are there too. For a second just consider the D700 without the vertical grip. This is a fairly small camera in terms of full frame offerings. The surprising thing is that an FM2 with motordrive is only marginally larger and heavier. Place an EL-e3a battery in the MD-12 and the weight actually goes down.
What the buyer of such a camera wants is not a million frames a second, or even 5 for that matter. They don't necessary want video capabilities or even live view (although admittedly that would be nice for critical focusing). Yes Nikon (or Pentax), you will be chastised by the internet reviewers for not including video, and all the other niceties of the modern uba-DSLR, but I don't know a single avid enthusiast who will not want that camera. Go beyond these requests (like doing all this in just a bolt on back with manual advance) and the Nikon fraternity will beat a path to your door. Well that's what I think at any rate.