What I don't understand is when everyone here claims the full frame can't be done, why not use the same basic body of the 6D without the mirror/viewfinder? No it would not be pocket-able - my sony nex 5n is not pocket-able, but it would reduce weight and size while still functioning just like mk111.
I wouldn't go to a job without two bodies in my camera bag I just would prefer if that second or third backup camera while having the exact same sensor characteristics of the main body could also be designed in it's own unique way. In this case as small as possible for those times when I want to go hiking, street scenes, video work, mounting in unusual places and don't want a full size dslr. (funny I use to strictly use a 4x5)
After using the sony nex I've come to one conclusion there are two size cameras one is point n shoot pocket-able and the second needs to go in a bag.
Here's my analogy (I'm not a golfer or a gopher) it seems Canon keeps making all these different cameras to be all to every use instead of making each camera body unique to help with specific problems. A golfer doesn't carry around a bag full of 9 irons or (do I dare:-) a bag full of woods. Nor is their putter manufactured significantly inferior to his driving wood because it's a lesser tool.
Yes mirrorless cameras are here to stay however I disagree they need to be a whole new system, but I'm only a photographer(tool user) not an engineer.
If Canon were to make a mirrorless camera using the same EF lenses, then it wouldn't be much smaller because the mount size/design remains the same and it affects lens size.
If Canon were to make a mirrorless camera using a new mount, then wide to normal focal length lenses might get a bit smaller, but the large aperture telephoto lenses will be nearly the same size. Anyone thinking that a 400 f/2.8 will be a lot smaller for a FF mirrorless camera than it currently is does not have reasonable expectations. One of Canon's advantages is its large selection of lenses available. Redesigning all the lenses for a new mount will take YEARS although an adapter can help lessen the transition pain.
I think Canon will eventually get to FF mirrorless bodies, but it will be a slow transition as technologies develop and production costs fall for the newer technologies (EVF at the same quality as the pentaprisms, etc.). The other issue is that APS-Cs outsell FFs, so it's natural that Canon would address that larger segment with the EOS-M first. I'd be tempted to get a 2nd generation EOS-M if it had improved AF for the wife and as a backup camera. For lowlight and shallow DOF, I'd want to use fast primes anyway and those are not pocketable anyway...