I know it is not related to the EOS-M system discussion, but an RF-S lens I wish more than anything else that Canon would make, is a modern mirrorless replacement of the "prosumer quality" RF-S 15-85mm. And yes, the 15mm is very important, but also give it some reach. If not 15-85mm then
at least 15-70mm. I recently had an accident with my old 15-85mm and afterwards photos had an
unsharp area in the right side of the lens. And while maybe not everyone would notice, it definitely annoyed me enough to stop using it. I tried using EF-S 17-55/2.8 and Sigma 17-40/1.8 instead, but while they definitely are good lenses for some purposes, they just wasn't anywhere near the 15-85mm as a
general purpose zoom. So I found myself suddenly bringing my Powershot G5 X II on all my casual walks instead of my EOS R7. I have a lot of RF lenses, but my RF mount camera was suddenly very uninteresting without the 15-85mm as my bread and potatoes lens.
I was lucky, I recently found a new good used copy of the 15-85mm. The seller claims he only (bought and) used the lens on a 2-week vacation in 2011. And I have no reason not to believe him. But better still, would be an updated modern RF-mount version.