You could, but it would add an extra layer of complexity. Either they call it RF and then have to explain in the small print that it doesn't give the FL/FOV you expect, or they create yet another line of lenses ("RF-S"). Casual consumers are already confused enough (the Amazon page for pretty much every Canon lens has dozens of questions 'can I use this on X camera?', even EF lenses on EOS DSLRs
). Mind you, Canon has surprised me before, I'm no marketing guru.
To me, the whole idea of a crop R body is weird. You can already mount EF-S lenses on the FF one. Creating a sub line of APS-C R bodies/lenses seems like unnecessary complication.