Is it size? Canon has made it obvious that RF lens designs on average don’t save any weight and size over EF versions.
I can see a niche market of solo operators who’d like AF/servo lenses that are parfocal with zero focus breathing (myself included). Targeting the R5/C70 crowd. But still, an EF version just gives the owner so much more flexibility with camera packages and ND adapters.
Canon should simply state that RF is it’s still/photo line of lenses and that EF/PL will remain it’s cinema line. And then release a line of very robust cinema-grade adapters for future RF mount cinema cameras akin to the 0.71x reducer. A passive mount, ND option, etc. all with 4x bolt-in points to quell any fears about adapter play.
RF cinema glass = great idea if Canon doesn’t want to sell many.