I am fairly skeptical of a FF EOS-M part coming along any time soon. With Canon's tepid entrance into the market, jumping into it again with another new EF mount (which I think would be required, lenses would have to be designed differently to get the image circle projected large enough to fill a full frame, with minimal vignetting, with the same EF mount) just doesn't seem logical. Not at this stage in the game. I think Canon would need to see growth in APS-C sized EOS-M cameras in the western markets before they, in their conservative ways, move on to make a FF version of EOS-M.
Personally, I'd welcome a better APS-C mirrorless from Canon. APS-C sensors are still relatively large in the grand scheme of things. Overall, they are the third largest general sensor size used in ILC type cameras, second largest if you exclude MFD from the pool. If Canon can improve DPAF, make it super fast, make it track extremely well, work in very low light, maybe even give it some more configurability...along with improved frame rates, IQ, all the standard stuff...oh, and give it a DSLR-style body design

P)...I think an APS-C EOS-M could be a success in western markets.
I'd be willing to buy a DSLR-styled EOS-M if it had great AF performance and excellent IQ. Let's just say, at a minimum, it would need 7D II/6D level IQ (preferably Exmor/NX1 level IQ) and none of the frustrating CDAF/PDAF funky-hybridized slowness and hunting that seems to occur on current DPAF cameras (or even, for that matter, on Sony A7 series cameras...their AF is decent, but still not on the level of dedicated DSLR PDAF unit performance.)