The first RF mount super telephoto lens will be a DO lens [CR2]

Hector1970

EOS 6D MK II
Mar 22, 2012
1,079
256
For the EOS-R to thrive Canon need to bring out a 1 DR and big whites. I'd agree a 500mm F4 or a 400mm F2.8 would need to come out for it.
I'd assume it would be late 2019 / early 2020 in time of the Tokyo Olympics which might be a real battleground between Japanese Manufacturers.
Professionals might be slow to adopt a 1 DR so it would need to be good and robust. Battery life needs to be good
You'll see plenty of 1DX II's and EF lens on sidelines for years to come.