The blue part above is the slippery slope. If R7 is a mirrorless 7D3 and that is all they offer with R mount + APS-C, they can (as others have said here) get away with just 2-3 crop RF lenses -- an ultrawide zoom a la EF-M 11-22, standard zoom a la EF-M 15-45 or 18-55, etc.
But they minute they cross over into the bigger / wider use-case / more varied userbases of general crop shooters (even at the 90D price point), there will be pressure to offer a proper line of crop-only RF glass -- they'll want small telephoto zooms, 60mm 1:1 macro, pancakes, etc. That's tantamount to double/triple dipping on EF-S and EF-M, and I think Canon would only go there if they intended to get rid of EF-S altogether. They will certainly eventually get to that point, but it may not be that soon. Crop SLRs still make Canon a ton of money, don't they?