EVF perhaps? There is also one extra contact in the lens mount, for power zoom perhaps?
Canon made a power zoom lens ages back (for the film 750 / 800's as I recall) pretty crap range (35-80) pretty crap aperture (mid max apertures) and no MF ring etc.
The interesting thing is that it worked on the exsisting EF mount as the servo and controls were integrated into the lens. Whilst I don;t think Canon will have (m)any legacy users this lens demanding compatability, I think it's evidence enough that a new mount needn't be considered to accomadate zoom lenses.
Of course if they were to move the servo controls to the body then it would be a different story. Personally, as a serious and frequent video user I would prefer the servo controls on the lens body (also restricts extra costs to those who specifically want video friendly kit) but above that I would also like zoom lenses that hold back focus through the zoom range, as many of the EF lenses do not (In this respect the push pull tele designs such as the 100-400 and older 80-200 f2.8 etc are actually brilliant for video)
I suppose the other issue is that if there is on body control then there can be off body control perhaps using something like the established LANC control (which gives prosumer camcorders rec start/stop, focus and zoom controls off camera, manfrotto and a few others make excellent integrated pan bar controllers) however this would require extra contacts between the camera body and lens, which would kind of pith off exsisting EF body and lens users.
Difficult one to call.
However I do like the compact form of this mirrorless. No sign of IS markings or switches on the lens... could they be in the body, or (unlikely) not there at all?