I don't particularly like this trend of slower lenses we are seeing from Canon. But I could make use of the 800 f/11. I shot my 400DOII/2x at f/8 more than at 560 or 400. I did all sorts of birding including BIF with that combo. I shoot at f/9 all the time with my Sony 200-600/1.4TC and that is for things like swallows in flight. For more static perched birds it is easy to shoot down at 1/200-1/400 with these newer IS/IBIS systems and most of the time (with a few insurance shots) you will get good results without motion blur.
I don't see much point in the 600/11....a 600/8 (which is also in the patent) would have made more sense so you could have versatility with the 1.4TC to go up to 840/11 if you wanted to but also have f/8 at 600 if 600 is enough. I've always felt the 600/4 lenses made more sense than 800/5.6 lenses for this same type of reasoning.
If the patent that was linked to yesterday
https://asobinet.com/info-patent-canon-800mm-f11-do/ in the other thread is accurate then we know about how long the lenses are going to be.
600/11: 335mm
800/11: 389mm
But those measurements will be to the sensor and not the mount so the physical lenses will be a little shorter...if someone knows the mount to sensor distance for the EOS R you can figure out the exact length (assuming the design didn't change from these patents). Those aren't super short lenses but decent size I guess.
But one thing that will be super important with these lenses for bird photography is BACKGROUND, BACKGROUND, BACKGROUND....forget about what your subject is doing...you will have to be watching your backgrounds and getting LOW, LOW, LOW for waterfowl shots if you want pleasing images....no f/4 to blast away messy grass/twigs etc. But that isn't a bad thing as the number one thing I see ruining bird images is not watching ones background and not getting low enough....even people shooting f/4 lenses suffer from that issue leading to mediocre images.