Either that or Canon has been releasing updated lenses with the (thus far silent) ability to work with new features and enhanced capabilities of planned future camera bodies that will use the EF mount.
I´ve been thinking a lot about this "mount subject". Especially since there is a patent for what I like to call an "EF mkII communication protocol".
As of today EF lenses are fully compatible with EF-s bodies. I.E. EF and EF-s mounts, use the same "pinning" and the same communication protocol.
If Canon decides to go with a "new" mount for FF Mirorless bodies. It would be the most logical, and practical, solution.
To go just the same way again.
Go with the "EF mkII communication protocol". And then either make it possible to use EF-lenses with our without some kind of "adapter".
Depending on what "lens-gap" they will use. That would make all existing EF-lenses usable.
It would also be possible for upcoming EF-lenses with improved performance.
I would actually be surprised if some existing lenses. Like the EF 70-200/2,8L IS III USM doesn't already have the "EF mkII communication protocol" built into it.