I know I am too late but hopefully this can be answered in the future somehow.

It would be cool to hear how quiet the electronic shutter is to the human ear when you're in the middle of shooting a wedding or in a room where a similar situation could be set up. DSLR's are super crunchy but the electronic shutter is supposed to be near noiseless.

That and battery life are the only real world tests I can think of that haven't been overly mentioned already.

Obviously everyone wants to know what the camera does when it overheats and how long of a cool down period it needs afterwards.

With the battery life the EOS-R5 is predicted to have I think I'll stick with my 5D Mark IV. I am trying to change batteries (as well as the memory cards) as little as possible when shooting weddings. I also carry two bodies for efficiency, which would make upgrading to the EOS-R5 from the 5D Mark IV that much more expensive. I wouldn't mind having that electronic shutter that the EOS-R5 has (listening to it on youtube videos it's almost noiseless) but that is not enough to jump systems (EF to RF).