Let me restate my position:
1. The Canon mirrorless will be a compromise. it will not satisfy everybody.
2. If FF mirrorless is so easily done, why there is only one FF mirrorless., M9 by Leica. Are Canon, Nikon, Sony, Pentax all dummies???
3. I want a FF mirroless also . But it is and will be either out of my reach or with features that I do not like.
4. What I really want is a reasonable priced Copy of M9, I would even be happy with a reasonable priced copy of M8. Both must be with M mount.
Realistically, even if the M9 were cheaper, the market for rangefinder cameras is limited, because most people want a camera with AF. - Leica has effectively stayed with the rangefinder design as a way around the fact that nobody has developed an effective AF system without a mirror. - Even Nikon's 1 series seems to be less than perfect in respect of phase detect AF.
I think so far none of the mirrorless offerings has really offered anything really revolutionary, because there have been too many compromises involved - particularly on AF, image quality and view finders.
I think most more serious photographers want a view finder for most of their work. I for one don't care whether the view finder if optical or electronic. What I care about is that it works. EVFs have left a bit to be desired thus far.
The NEX 7 has probably come closest so far in terms of these compromises, but it is hobbled by being a Sony with the inherent lack of available lenses and accessories. - A good Canon or Nikon mirrorless would benefit from access to a huge selection of lenses (via an adapter), good flash equipment and other accessories, which Sony cannot.
I would be prepared to settle for an APS-C sensor in a mirrorless camera, but it would also need a decent viewfinder, decent AF and an adapter for my EF lenses plus the ability to use an ETTL Speedlite.