Canon will soon announce the EOS R3 (Development announcement), RF 400mm f/2.8L IS USM Lens, RF 600mm f/4L IS USM lens. According to CR, Canon is working on more super telephoto lenses for Canon RF mount. Below are rumored lenses coming next:
Canon recently has filed a new lens patent in Japan. This patent is for 400mm f/4 DO lens, 600mm f/4 DO lens, and 800mm f/5.6 lens. The patent didn’t mention whether this lens is EF mount or RF mount, but hi-lows-note said these lenses could be RF mount, and upcoming EOS R could have IBIS.