With an (Let's call it RF-S) mount, I see no reason to keep the EOS M line going. They don't have very many lenses anyway and they can simply tweak existing optic formulations for the new flange distance and mount. I don't see it being super resource intensive. I see replacing the M line as a good investment if Canon is to take the mirrorless game seriously.
Again, wow, let's ditch that damn EF-M mount.
Why, for God's sake?
Because YOU think it's useless?
Do you honestly imagine the only reason Canon created this mount was in case they wanted to create a 7D successor on it?
It's evident from the huge number of people buying EF-M that it's far from useless to a lot of people. Canon makes a ton of money from it, even with the limited lens selection. It's not going away. OK, it's not going into your camera bag either, but that doesn't mean it should go away.