I don't think that any successor or replacement for the 7D will be incompatible with EF-S lenses. That would just drive a lot of near-certain buyers down to the 70D.
So this brings up two interesting questions:
1. Would a 1.3x crop mirror clear the back of all of the EF-S lenses? If so, they could just crop the image when an EF-S lens is attached.
2. If not, how many of Canon's EF-S lenses have a back-focus distance that's short enough to force Canon to disable them in a 1.3x crop?
Of course, I keep wishing Canon would build a dual-mode full-frame/crop camera with a slightly more complex mirror assembly that slides out of the way of an EF-S lens before it flips, but....