Hmmm....maybe my physics is more than a bit off
Just as a broken analog clock shows the correct time once in every 720 minutes, you've finally managed to be correct about something. Well done!
OKIE DOKIE --- Like I said, Optical Light Path Physics is not exactly my strong point, but what I AM CURIOUS ABOUT...is it or is it not true that the Canon 7D Mk2 contains a sensor that allows for a focal plane distance of anywhere from 25 to 44 mm if an adapter was able to be used?
I simply don't know how it could be done BUT I do wonder based upon YOUR professional medical/optical experience and opinion .... if it is at all possible (beyond any Canon financial or product lineup issues!) to create a box-like camera as thin as 27 mm with a lens bump containing what I am assuming an EF-S mount allowing for an APS-C sensor size to actually work in a mirrorless configuration.
CAN IT BE DONE?
What are the light path physics behind your yes or no answer?
Why do I bother?
The flange focal distance doesn't really matter as far as the sensor goes (notwithstanding the angles of refraction of the microlenses, but that affects IQ not whether an image can be focused on the sensor). The FFD does
matter for the lens, and a lens must be designed for a specific FFD. If the FFD is too long or too short, the ability to focus the field image on the sensor is impacted (at one end of the range, e.g. infinity focus is lost, or throughout the focus range).
Your ridiculously sad photoshop mockup shows an EF-S mount, and all lenses designed for that mount (EF and EF-S) require a 44mm FFD. Sure, you can stick an adapter on a short FFD mount for compatibility with lenses that have a longer FFD – that's exactly what the EF EOS-M Adapter does, allow mounting EF/EF-S lenses with a 44mm FFD on a mount designed for EF-M lenses with an 18mm FFD. But the EF-M mount is a different mount, with different lenses. The mockup shows an EF-S mount, but if you mount an EF/EF-S lens on that mount, it will not be able to focus an image on the sensor, because the sensor is too close to the mount.
Your suggestion of an adapter is a red herring, thrown on the path post hoc to distract from the fact that the mockup is a fcukup. If the fcuked up mockup had a completely novel mount – let's call it the EF-BS mount (I think you can guess what BS stands for) – then you could sell the idea of really short FFD lenses for the EF-BS mount, like the 'glass cover adapter' (although that's another physics fcukup on your part, it would have to be a lens of some sort to form an image on the sensor – you really should have gone with a pinhole lens cover there). That would also allow an EF-BS mount adapter for EF/EF-S lenses.