The big problem is unless you use fisheye lenses like 6 or 11mm full frame (35mm equivalent), the full frame equivalent focal length you get with the HQ camera

The big problem is unless you use fisheye lenses like 6 or 11mm full frame (35mm equivalent), the full frame equivalent focal length you get with the HQ camera sensor is practically in the exotic telephoto range, it's a crop factor of like 5.2x. It's nice for things like astronomy (your nice 200mm f/2.8 is now 1000mm+) or bird/nature watching, but it's highly impractical for anything but specialist portraiture or walk around use. Most of the c mount lenses available are pretty poor, and getting focus right with anything not way stopped down (especially without a large display) can be super tricky.