I've been a working pro for nearly 35 years. One feature I would love is a shortened shutter response mode. Something akin to 6ms response from shutter trigger (this has nothing to with shutter speed). Canon actually built a camera like this in the film days - The Canon EOS RT and EOS 1N RS. It used a pellicle prism so no mirror had to be lifted out of the way to make an exposure.

Why would anyone want this? Let me show you how I photograph wild bats in flight at night. I have many other use cases. For now I have to mount a shutter on the front of my lens to gain back the shutter response that i use to utilize from these film cameras of old.