Yes, I have to admit I've been looking at these. Currently I used a 7D mkII and 100-400mm f4.5-5.6 L IS II as my main walk around set up, plus a number of other lenses and bodies. The 200-600mm f6.3 looks amazing. The internal zoom is the main feature, because in practise it's almost impossible to zoom in an out when something like a flying bird comes closer than expected. It seems sharp at 600mm, and there are other little features like the tabs either side of the lens for carrying it. This A7R IV gives 26.2mp in crop mode and it gives the buffer 3x the limit. With the high resolution EVF this is going to make an incredible portable wildlife set up.
I'd like to think Canon were going to match this because I'm very invested in the system, for instance I have 7 Canon fit macro lenses. However, there seems no good reason to think that Canon are going to introduce something competitive in the next few years. Like yourself 10k+ lenses are out of the question, not just on price, but on portability.