Couldn't Canon make a mirrorless camera with EF mount and a shorter flange distance?But why make it EF mount at all then, since an EF adapter is basically just an extension tube. I mean, look at the patent, it's an extension tube with electrical contacts
Lenses for the mirrorless camera would not focus on other cameras with EF mount, so some special designation like EF-ML would be required, but regular EF & EF-S lenses would mount using an extension tube with contacts.
The only reason to make it EF mount would be so people could use EF lenses right away with no adapter...once you add anything between the lens and the camera, you might as well optimize it for the target market (in this case, small camera with small flange distance). If the EF-ML lenses don't work on DSLR's anyway, there is no reason to build them around an existing idea, especially if something completely new is simpler and smaller
If the mirrorless camera uses EF mount with the same flange distance, the camera would necessarily be bigger (at least thicker), and it would be harder to design ultra wide lenses for it.
If the mirrorless camera doesn't use the EF mount at all, Canon would have to quickly release a big set of lenses, or the camera would be of limited interest.
Canon can choose an existing bayonet, say Sony E-mount, but then (a) owners could buy non-EF lenses, which is not as profitable to Canon, and (b) the camera wouldn't be as attractive to existing EF lens owners.
Furthermore, lenses with larger focal lengthes and/or max apertures wouldn't be any smaller, similar to the situation with crop bodies & EF-S lenses, so there isn't much sense in designing & manufacturing new models, when it's possible to use existing EF lenses with a simple adapter.