This makes a great deal of sense. The M series lenses have a width restriction (at least, so far). It's a design decision, not a physical constraint (Tamron, at least, makes a fatter 18-200 zoom), Canon would either have to get over this, or convince people to use an adapter. As for the weather sealing, nothing would preclude them from coming out with a weather-sealed model in the future.I don’t think the M series aims to ever be used as a 7D line replacement. Canon doesn't seem to market them as weather sealed at all, meaning they probably aren't. And if they stick with the 63mm lens diameter for all Ef-m lenses, we'll never see a super zoom or anything remotely fast and long in the native mount. We've also not seen a dual card slot M camera yet.
The 7D people seem to be looking for something withstanding harsh environmental conditions that can be used reliably and comfortably with long lenses, mainly for wildlife. The premise of keeping size and weight to an absolute minimum while keeping the price reasonable does not seem compatible with that.
And to--for the moment--broaden my scope a bit, the R is almost weather sealed...apparently the viewfinder is the main flaw here.