I'm not sure I completely get what you're saying here. They get a selection of native glass whether they go M or R, they can attach their EF lenses to both bodies.OK, this is a much more logical take in the context of Canon.... but I still don't see the upside for a 7D2 shooter, outside of the..... "opportunity"..... to buy some expensive and exotic RF glass. The ability to use all their old EF glass and LP-6x batteries while also getting a small selection of native mirrorless glass seems like a win-win for the user. Maybe I am looking at this too logically
With the R they can take their batteries. With the M they cannot.
The R has more lenses that appeal to a birder or a sports shooter which is using a 7x series.
And they get the same balanced body / ergonomics / layout on a new R body.
Potentially for both bodies (ignoring heat):
They get a better sensor (both size, 32MP, and DR). They get a slightly faster fps.
Most importantly, they get Animal AF.
If they price it in the same range as the 7x was sold for with NPV, then what's not to like? Take all your existing kit, get a more modern system, better AF, cleaner images, subject tracking, plus the opportunity to add a lightweight 600mm or 800mm lens for less than a grand.
Is that any less compelling than the R5 and R6 for existing FF dSLR users?