Haven't had a chance to try out the camera itself (stores being closed due to COVID-19 and all) but the output from the R5 is certainly impressive. I'd rate the output quality alongside the A7r4 and D850, with little to distinguish between them (the 61MP on the A7r4 doesn't usually add as much as the 16 extra megapixels would suggest, unless conditions are perfect). The R5 output seems a little easier to work with for colour portraits; for landscapes, they're pretty much the same.
Up until the pandemic, I would have said there would probably be a 5D5, and possibly even a 5D6, but very few further SLR lenses. There are a huge number of SLR lenses and SLR users out there, who, even if they aren't adding further SLR lenses to their collection, would still be keen to keep using their SLR lenses for one or two more generations, until the lenses start to wear out or get superseded by newer/sharper/lighter technology.
With the pandemic and subsequent economic downturn, however, I'm not so sure. Doubly so if the already-delayed Tokyo Olympics end up being cancelled entirely. Any further 1D- and 5D-line releases would be about catering for existing SLR users, not attracting new ones. Canon may just decide to cut its losses and concentrate on the mirrorless line which represents its future, rather than putting further resources into SLR.