The C70 & speed booster are obviously aimed at shooters with existing Canon EF glass rather than those of us wanting to go all RF glass. The EF 24-105mm f/4L IS II USM is the same price (on B&H) as the RF 24-105mm f/4L IS USM but the "native" RF lens will have a crop factor. While I'm excited about the C70 there is still the issue that the Super 35 sensor negates some of the value of RF lenses. I own the RF 28-70mm f/2L, a much nicer lens than the three EF lenses compatible with the speed booster, but it becomes something along the lines of a 48-120mm with the Super 35 sensor.
I suspect Canon will eventually release this camera body with the R5's 8K full frame sensor, but not until they have more RF mount cinema lenses.