As a result, the inevitable transition from DSLR to mirrorless should be much less painful (and EOS lens depreciation much slower) than in the case of FD-EOS transition.
Having painfully gone through the FD/EF transition, I can certainly see this next transition being much easier. Although I hated it at the time, I now find reason to applaud Canon's foresight in creating the EF mount. It will even make this inevitable transition gracefully.
The advantage of being the big dog on the porch is that when a smaller dog brings in a juicy bone, the big dog can take it. Remember that Minolta caught Canon totally by surprise with autofocus and had a three year head start...but Canon took that bone from Minolta anyway. Raw manufacturing and marketing prowess counts.
The only company Canon has to fear is Sony, and Sony tends to shoot itself in the foot often enough.
That would be the Olympus OM-D, with the form-factor of an SLR...but no mirror inside and sporting an LCD in the viewfinder. The problem with the OM-D (IMO) is that Olympus is unfortunately wedded to the Four Thirds sensor.
But something along the same lines would be an easy transition concept for Canon, starting with the Rebel series.