Originally posted by Paul the Sunman As I said, I prefer an optical viewfinder, certainly over liveview. But the shear size of the 645 ensures it will always be a small-volume seller. Nothing wrong with that if Ricoh can still make money on it and maintains its enthusiasm. However, if you could get a MF sensor in a mirrorless body not much larger than a current FF camera, and at a price of say $4k, how would that sell? And to whom?
Depends on what you meanly FF camera. The market for FF is effectively split into 4 camps now:
1) Pro size like the D4
2) Prosumer size like the D800/600
3) Mirrorless size like the A7
4) Compact size like the RX1
The volume difference between a 645 and a D4 isn't huge. I used to have a Mamiya kit and a D700 and the Mamiya (about the size of the 645z but much lighter) and the medium format was a bulky, tripod pig comparatively.
So what you are really describing is a Leica S without the mirrorbox.
Compare camera dimensions side by side
If you really want to make the most of a reduced size body to take on the prosumer D800 size, I think a mirrorless MF will have to make some compromises. I suggest (and I'll sound like a broken record here) that achieving smaller body size will also require a midst of smaller lenses; letting mirrorless really be mirrorless.
Collapsible lenses, like the Mamiya 6 kit would be the way to go. Problem is, as a "system" camera, you will maybe only ever have 5 lenses in the product line. If you've ever seen a Mamiya 6 collapsed you'll get what I mean: