@bwv812 wrote:
There would likely be significant registration problems, not to mention dirt and sensor fragility. But there's also the problem of powering the sensor and knowing when to begin/end capturing. I mean, while you could use the film-advance mechanism to know when to switch to a new exposure, the back has no idea when the shutter will be pressed and has to be constantly ready for the mechanical shutter to open, unless you want to keep turning it on and off. The image processing and digital specific hardware would probably result in something looking like even less elegant versions of the bulky old Kodak and Fuji DSLRs based on Nikon's film bodies. I suspect the target audience would be tiny: those willing to pay the high prices inherent in full-frame sensors, but who have a big backlog of old lenses from obsolete mounts they've yet to move on from, and who don't need that much in the way of reliability and durability.
I'm not sure anything in old bodies is undervalued. The light-tight box aspect of digital cameras probably isn't that large a component of their price.