[Klaus]

Canon patented an adapter with cooling capacities
https://petapixel.com/2020/07/27/canon-patents-eos-r-lens-adapter-with-active-cooling-built-in/
but IMHO the last thing a videographer wants is a noisy fan that might also add some shaking......
what do you think ??

It all depends on the degree of noise.

Regarding the patent - I'm slightly wondering whether 
* front cooling will suck in dust where you really don't want it
* front cooling is less efficient than rear cooling. I suspect that the protection glass / AA filter is a good isolator