That RF 800mm (and the 600mm) is a brilliant idea for a lens.Canon announced three new lenses, including the RF-S 10-18mm f/4.5-6.3 IS that I have been awaiting for a UWA solution for my R10 crop body. The lens is quite a bit smaller than the old EF-S 10-18mm and is fairly inexpensive ($329), which works well for me. I plan on picking one up soon. This should complete my mirrorless lens lineup for the foreseeable future.
Canon also announced a RF 200-800mm f/6.3-9 IS and RF 24-105mm f/2.8 L IS lens. The 200-800 is interesting, but at 4.5 lbs. and $1,900 is not something that works for me. My RF 800mm f/11 IS weighs 2.75 lbs. and cost $900. The RF 100-400 meets my telephoto zoom lens needs in a small, light weight package.