[davidmanze]

1:
First, Canon already has 600mm f4 and 800mm f5.6 lenses to mount on any EOS R camera, it is not as if RF mount lenses like that will be smaller or lighter, just because of the mount differences.

2:
If this rumoured 800mm f11 is inexpensive and comparatively lightweight, it does make sense. The loss of sharpness due to diffraction can be mostly compensated by Canon's DPP software with the appropriate lens profile.
How a 600mm f11 prime from Canon will have to compete with 3rd party 150-600mm zooms, not sure. We will see which lenses actually will materialise.

3:
And the donut bokeh of mirror lenses is due to the mirrors, not due to the small f-number ;-), Dave. And how often do you do your birder thing when it is not bright and sunny? ;-)

  3:  I think I know mirror- lens doughnut bokeh is down to the mirrors BC .. really !!
...... the inference was "is it a mirror-lens?"  (tongue in cheek joke ha ha!!) ....... which of course it won't be .....

 I go birding when it's sunny mainly yes for the pop !!...... and as I said the 600/800mm F11 will only usable in sunny weather (for anything that moves) .......
....... but the G2/Sony/Sport is 1 2/3rds stops brighter at 600mm ..... and at 150mm it's 2 1/3rd stops brighter ...... that's huge BC !!  .... and the difference between 600mm and 800mm isn't !! .. 
 Those who chose the Sony 200-600mm will be getting the best deal as the their 1.4X TC hardly drops the IQ and you get a 840mm F7.1 lens.

 How can you argue with that ??