Canon has had their foot on the gas ever since the release of the EOS R5 and RF 28-70mm f/2L USM lens. It looks like they have no intention of slowing down, with two mightily impressive lenses likely on the way soon.
Digicame-Info discovered two lenses that have been added to dealer lists recently, which indicates an imminent release. The lenses are the RF 800mm f/5.6L IS USM and RF 1200mm f/8L IS USM. It is no surprise that an 800mm f/5.6L is coming to the RF mount lineup at one point or another; the EF version has long topped out the revered line of professional supertelephotos that ranged from the 200mm f/2L up to the aforementioned lens. As such, an RF version has likely been planned for a while, and now that the RF 600mm f/4L IS USM and RF 400mm f/2.8L IS USM are available, it seems a logical next step.
On the other hand, we have not seen a 1200mm lens since the famous 1200mm f/5.6L, and that lens had an extremely limited production (it's rumored that only about 20 copies were ever made). As such, a new 1200mm lens could be quite exciting and would be a very interesting offering for a range of photographers. We'll see if the next few months bring an announcement!