I still would like a hi-end FF mirrorless "with everything": very compact fully weathersealed body, excellent sensor, very fast phase-detect AF on the sensor, and an electrified Leica M-mount which would be both compatible with manual focus M-Mount lenses as well as with new nanocoated AF-lenses build specifically for it. At the price of say a 5D3, rather than a Leica M9 (which I do not want for a number of reasaons, most importantly that itr is a manual-focus only mechanical rangefinder, and the only thing digital being its sensor).
Canon could give me that ... if they only wanted. But, they do not want. Unfortunately.
On the other hand: I do not want consumer-oriented viewfinderless point and shoots like this EF-M. Even if it has an APS-C sensor and not only a puny G1C 4:3 sensor. If Canon won't serve me
I wont buy their crap. As easy as that. Somebody will eventually build the camera I really want.
As has been pointed out, it looks like the diameter of the EF-M mount will accomodate a 24x36mm sensor. I don't think the technology is there yet to accomodate all the needs of a user of a full frame mirrorless camera, but I think the balance of probability is that some day we will see it. For now, you are better served with a DSLR. Give it 5 years, and things will look very different, the technology required to deliver in-sensor PDAF and a decent EVF will have evolved. Electronic shutters will probably also develop a lot more in the next few years.