I am not sure that a mirrorless camera inside a bulky DSLR body using DSLR lenses is what Canon (and Nikon) need. They will have to introduce the new mount and a whole new range of lenses that require shorter flange distance in order to make their bodies and lenses more compact and competitive. Otherwise Panasonic, Olympus and Fuji will eat them alive.
They already did that. On Canon that is the EF-M mount, and I forget on the Nikon (the Nikon 1 line). This puts them in line with Sony which has the Alpha DSLR and NX mirror-less.
One barrier to replacing the DSLRs is existing lenses. to get rid of DSLRs, I think you will need to be able to full exploit existing lenses. Also I, for one, like large bodies that provide good grip and lots of buttons (note: Panasonic, Olympus, etc all put out SLR-sized bodies too). The major hurdle has been the fact that lenses designed for phase focusing (which I prefer) are not well suited to contrast focusing; and phase focusing on a mirror-less has been basically non-existent. Therefore: even though there's an EF to EF-M adapter: the cameras have not been able to fully control the lens.
A big advantage of a mirrorless system is more compact lenses that allow better IQ for the same manufacturing costs, if done properly. Look at Fuji - their APS-C lenses are already better than anything Canon or Nikon can offer for their cropped cameras.
Really. Wasted my money on my 70-200mm L did ?
Switching to a mirrorless range effectively means for Canon/Nikon killing their DSLR cameras AND LENSES, and probably that is why they are hesitating.
I think you have it backwards. The lenses (and focus) are what are keeping SLR's afloat. Cannon, Nikon, Panasonic, Samsung, Sony, etc all offer mirrorless alternatives *now*; yet SLRs are still around.
Even if we just abandoned SLRs for mirrorless tomorrow (without creating proper compatability): Canon and Nikon are still lens manufacturers in that arena as well.
Personally: I hate the kit lenses on the Sony NX. Not because of image quality; but because of controls.