Yeah it's been discussed a few times...
I have to say that a totally mechanical digital camera won't happen. Ever
But I think heads would turn if a manufacturer built a solid, metal frame camera with nothing but the shutter release button and the exposure triad (aperture in the lens, ISO (call it ASA for bonus vintage points!) and shutter speed in the body). Plus a light meter. Bonus points if it's a needle in the viewfinder
No back screen and I wouldn't even have a winder (why??), just an indicator in the back of how many frames are left in the card. JPEG engine with an AUTO (green) mode that would just pick whatever settings it found right, or maybe a button where you could scroll through various film emulations and just pick the one you wanted (with an option to lock the ASA to match the film). 24x36mm sensor and viewfinder, of course... and if it's a Pentax, it has to be K-Mount
Might be a cool off-the-beaten-path product and wouldn't have to affect that manufacturer's regular product lines in any way.