Again with lenses I'm out of my element since I'm not a video guy. I'm not sure what you mean when you say the lenses "use technology that is existing in the canon line." While I'm sure some of the optical design can be borrowed the result must be parfocal, and it's my understanding that a lot has to change regarding the chassis in which the optics are mounted: it must be optimized for manual focus and to eliminate focus breathing, etc.
I don't pretend any expertise, just enjoying the speculative conversation. It seems to me there's a bigger difference between a still lens design and cinema design than between FF and MF.
The Canon CN-E primes appear to be VERY similar optically (if not identical in some cases) to their L counterparts. The cinema zooms are obviously dramatically different designs, however.
Medium format lenses have to cover a much, much larger area (while still autofocusing...) so while the optical designs might resemble scaled up stilll lens designs more than they resemble cinema zooms, they would have to be pretty much all new.
My [mis?]understanding of the motivation behind film MF was the limitation on how much film could be enlarged. MF lenses weren't as sharp as FF lenses, because MF film wasn't enlarged in printing as much as FF film.
As example, FF film was always enlarged 16x area just to get 4"x6" from 24x36 (mm) film, while 8x10 film (large format, I know, just illustrating) was printed 8x10.
So, how useful would MF lenses from the film era for digital MF sensors? Wouldn't the manufacturer have to make an all new line of sharp-as-FF lenses for the new sensor anyway?
Film enlargements might be based more on grain and film sharpness than on lens sharpness, but lens sharpness had to be sufficient for enlargements, too. In my experience, fine grain 135 ("FF film") can be enlarged to about 8''X10'', maybe a bit larger; 8X10, while often contact printed to 8''X10'' can flawlessly be enlarged to about 80''X100''... The ratio is always about 10 times in each axis for irreproachable quality, but it's a little smaller for smaller prints due to the viewing distance. Black and white grain looks nice and scales up nicely, however, to larger sizes. I think FF digital can easily scale to 11X17 and I am sure soon MUCH larger; it is on par with good 6x7 medium format in terms of sharpness but with less grain and also less resolution.
The thing is, those 6x7 lenses had to be adequately good wide open for film... meaning they are often stellar stopped down. The 50mm f1.4 Nikon AI lens is not great wide open on digital (the Otus is surely better), but by f5.6 it is still good enough for digital, especially for APS-C. 6x7 lenses stopped down will be perfectly sharp for high pixel density digital. Large format lenses are a bit softer.
Irrelevant... Canon will never go in this direction!