jolyonralph said:
As I said before, there will be EF mount or EF-M mount, I think it's almost impossible Canon will go for a third incompatible mount system. Once they start doing, for example, cheap 50mm lenses, they'll want them to be sold to APS-C shooters as well as FF shooters, so the mount has to be the same.
There is no "incompatible" mount. Canon will simply move from 2 mounts in the mirrorslapping past to 2 mounts in the mirrorless future. 1 FF mount, 1 APS_C mount.
1. EF -> EF-X ... "full frame" image circle; full backwards compatibility with EF glass via simple adapter; functionality within limits of legacy EF glass - especially for AF, but also other more advanced functions; "wireless E-TTL II with second curtain snyc" for example ;-)
2. EF-S -> EF-M .. for APS-C. transition almost complete already. Not many more EF-SS lenses to come. Except an 18-55 kit lens with lens LCD display, maybe
Only during multi-year transition period will there be "4 versions of mounts" - 2 old, 2 new. Evrything cross-compatible within reason [lenses need to cover image circle].
Canon does a separate mount for APS-C and FF also with mirrorless because it has worked so well for them in the past. First, people run out and buy "entry level" APS-C cameras and APS-C lenses [EF-S]. Then they upgrade to "full frame" cameras and lenses [EF]. Then they add mirrorless APS-C cameras + lenses [EF-M] for small size. Then they buy full frame mirrorless cameras and lenses ["EF-X"] once Canon launches them.
End result: Canon has cashed in 4 times on the same customer set.
;D
Even me, a typical, highly representative, well-informed, good-looking, critical and smart Canon customer has completed the first 3 steps in this lemming cycle already. And looking forward to take the 4th step too. Stupid me. LOL.