Originally posted by Na Horuk , to see if Pentax can maybe make their own retro DSLR
IIRC the thing Nikon went to a lot of trouble to do was to ensure that the Df would work "properly" with all the ancient lenses. And there is only one way to do that for a Pentax DSLR, at least insofar as K-mount glass is concerned.
Now if you wanted to make a camera that would seamlessly handle both K and M42 with full aperture reading of both K and SMC Takumar lenses and auto stopdown on the M42s, yeah, that would be too much of an ask. I suspect you would be looking at the loss of shake reduction to fit all the aperture-reading gear back in, and almost certainly the SDM/powerzoom/DC contacts as well. Whether you could keep even the screwdrive motor would be touch-and-go; I suspect the M42 flapper plate would get in the way there.
OTOH if you wanted to limit yourself to merely handling all the K-mount lenses seamlessly, then you can keep the screwdrive (and if you build an M42-only DSLR you don't need it). I can't recall off the top of my head whether any of the film bodies had both the aperture arm and the power zoom contacts, but if you can do it with film, you ought to be able to do it with digital (although again, can you also keep the shake reduction mechanism?).