Don Haines said:
... the assumption that when Canon goes mirrorless that they will both discontinue (eventually) mirrored cameras and that the new mount will be a much shorter distance... This assumption may not be correct.
...
Canon said it was going to be an elegant solution....Throwing out everything to start again is not an elegant solution.... an elegant solution would be to keep the existing mount and upgrading the firmware/hardware on new lenses/cameras to accept a higher speed camera/lens data pipe and more lens computing power to give better AF and IS performance..... and allow you to mount crop lenses on the FF camera. The elegant solution could also include a dock like sigma and Tamron to reprogram lenses (or use a tethered body) to adjust lens parameters......
I can think of four different solutions to the mirrorless FF mount problem:
(1) EF-M variant that requires an adapter to mount EF lenses. Not exactly elegant.
(2) EF as is with just internal changes like you describe (or rather EF-S to allow mounting crop lenses, too). I don't think this is particularly elegant either.
(3) A new EF-compatible mount, similar to EF-S in that it'd allow mounting EF lenses directly but also new EF-X lenses that'd protrude much deeper into the body. Short focal length EF-X lenses could all but disappear inside the body keeping the combination small, and there'd be no need to do anything with longer lenses. That would be an elegant solution in my view.
(4) A combination of the above: big bodies with EF-X mount as above and small bodies with EF-M2 (or whatever, EF-M compatible) mount plus an adapter that allows mounting EF and EF-X lenses (maybe EF-S too). This would have the potential to make everybody happy, though it'd require maintaining two lines of short lenses (EF-X and EF-M), but that's nothing new.
I'm kind of hoping for (4).