If the lens ends up being f/5.6 @ 400mm, in a sense it's basically a 100-400 with some additional reach tacked onto the end at the cost of aperture. Treat it like your 100-400, where the aperture "limitation" hasn't stopped anyone from creating excellent photos. If it ends up with similar performance (IQ and AF speed) and MFD as the 100-400II, and costs roughly the same, I believe this will be a great piece of kit if you're staying in the Canon system.
Who cares what Sony, Nikon and other manufacturers do, I get it, but it has to be said that for a while now Canon has been lacking a XXX-600 offering to compete with the Sony 200-600, Nikon 200-500, Sigma 60-600, Tamron 150-600, etc. because that's where it's at right now for affordable super-tele range lenses. 600mm at f/6.3 is gobs more useful than 500mm @f/7.1, especially if you're aiming to shoot birds/wildlife. Yet, Sony splits up their tele offerings w/ their 100-400 + 200-600, so maybe some of these Canon patents will come to fruition and they'll get out to 600 or 700.
The 600 and 800 DO f/11 lenses though... um.... I'm sure they'll be nice and compact, but f/11 is severely limiting unless you're shooting in bright, midday light, which is rarely the case when capturing birds or wildlife. Forget about Golden Hour, the high ISO noise will be ridiculous. "well, the R5 sensor may have better high ISO performance"... just no.
Here's how I'd play it for the RF line:
80-400 f/4.5-5.6 - $2100
200-700 f/7.1 - $2600
600 f/6.3 DO - $3500
800 f/8 DO - $4200
And then offer the usual 300/400/500/600 f/2.8 and f/4 lenses, increasing in price from $7000.
Ultimate wildlife/birding + sports spread, you'd essentially have 4 "consumer grade" super tele lenses that would offer unique capabilities or features without fear of obsoleting another lens in the line. Not only that, each are compelling enough that you'd have people buying more than one of them. A 200-700 would silence the Sony/Sigma zooms, and the DO lenses would take care of the Nikon 500 PF, while at the same time protecting Canon's super-tele f/4 line. The market is there for these sorts of lenses, just do it already, Canon.
As a Nikon 500 PF shooter, I'd come back to Canon in a heartbeat if the even remotely tried to compete in this arena (an 800mm f/8 DO on FF would be absolutely perfect), but f/11 is just not realistic. I hope the f/11 is incorrect, and they pull a last second switcheroo and make it f/8.