I think the aim here ought to be to make something that works well and really feels right in the hand, in an FM2 kind of way, but with things like modern metering.
And here it's appropriate to consider the body as well as the lens. Nikon showed with the D750 they could make a DSLR smaller than anyone else if they wanted to; it's incredibly shallow from the sensor plane to the back of the camera because of where the logic board is inside the camera, and that makes for a smaller body and a surprisingly deep, comfortable grip for such a small camera. Suppose they simply applied those techniques to the Df, now without the big AF-style grip, which would knock probably 5mm off the depth of the camera and 5mm off the height.....and now, suppose they replace the remaining AIS and AIS-derived AF lenses with a new line of optically high-performing, small f2.5 and f2.8 primes with AIS-standard ergonomics, AIS-style dimension, and the new, smaller, quieter AF-P autofocus motors.
Wouldn't that cut into mirrorless? Wouldn't that sell well? They'd probably have some decisions to make, such as whether to make it purely about stills like the Df or include multimedia capabilities (I'd favor the video, to gin up sales a bit), and whether to retain the mirror or go mirrorless with an F mount. But still . . . . . done right the whole rig could be barely bigger than the Fuji mirrorless bodies, about the same size as an FM2, and compatible with the entire Nikon lens line.
