Why would canon develop a FF slr that its still in general the same size as the 5d,6d body size and keep the lens mount and distance to the sensor the sameAs far as I can see the reduction of body size is a bit overblown especially for FF as the lenses still need to observe physical limitations. Sony's FF lenses are evidence that the masters of miniaturization cannot skin that cat.
This gets to market segmentation. You have multiple users of mirrorless with different needs. Consider just two (of many) groups coming to mirrorless from SLRs:
1) People who love the small form factor for carrying or discretion reasons — street, reportage, travel shooters and such. They *don’t* want big lenses, huge grips and such. They want 90% the IQ/features of a same-sensor-sized-SLR in 50% of the size.
2) People who are migrating to mirrorless from DSLRs simply for the best IQ they can get (i.e. people buying the various a7 Sony models) — a good example would be Canon landscape shooters wanting more MP or more DR. These folks don’t give a damn about form factor and are bolting big L lenses on to these bodies with adaptors. Effectively, they *aren’t* mirrorless devotees so much as fans of wonderful sensors and don’t mind fighting through the limitations (battery life, AF, etc.) of today’s mirrorless rigs. An A7R and an adapter is a much cheaper way to upgrade your sensor than buying a D810 and new lenses.
Normalnorm, it appears to me that Group 1 above really cares about size, and Group 2 couldn't give a damn if it takes the best shot (and, bonus, lets them keep using their old glass).
I think -- just maybe -- that the complexity of the user's needs in mirrorless might scare off Canon and Nikon as (at least for now) being a bit too unpredictable to make a major investment -- i.e. should they aim their mirrorless efforts at fully replacing what DSLRs do, or should they focus on getting the size down? Doing both could be irresponsible w.r.t. time & dollars.