As long as we're blatantly speculating here, the opposite possibility is that they'll push ALL APS-C towards the M mount (they'd need more EF-M lenses to do that, though, and those lenses would have to be of greater diameter than the ones so far). They've already got an enthusiast body for the M, so it seems to make some sense that they could start doing enthusiast lenses for it, in addition to the lenses intended to be compact (making larger lenses wouldn't negate the ones that are out there already). (At this point,, someone is going to jump in here and tell me that "marketing" has decided that no matter how awesome an EF-M camera might be it's targeted to beginners. To which I say, 1) you don't know what they're thinking, 2) "marketing" can change their mind and decide there's an opportunity in making the M series more enthusiast friendly, and 3) we don't know that they haven't already changed their mind and such lenses are in the pipeline.)I think Canon will eventually (and I mean in several years) switch over the Rebel line to the RF mount, and also create a 7D equivalent in the R series. Along with that, I think they will create RF-S glass for those APS-C sensors. If that happens, RF-S will be in direct conflict with M, and M will lose that battle. Obviously all heavy speculation...but just my two cents.
With those additional lenses, it would be doable, the only people left hanging would be some in the 7D crowd. (Some would be satisfied with an enthusiast M camera and adapting EF and EF-S lenses.) And I suspect there could be a hi-res R camera out there with a mode to "pretend" it's an APS-C for the benefit of very high-end users of APS-C. That would allow them to use the RF lenses that they're pining for while still keeping their crop factor (and relatively smaller file sizes). The downside, of course, would be bulk and expense; they'd be paying for a full frame sensor they don't have as much use for (though they might find uses for it once they have it).
On the R end of things I see room for an 83 MP High Res (their 32MP APS-C scaled up to full frame) and something in the 40-60 MP range as a "mid res" (still higher than almost anything else they have). With a lot more speed than the present-day sensors!