Originally posted by Fogel70 KAF3 is already in use (used on lenses with AF-motor and no screw drive).
I believe they would have to design two new versions of the k-mount to implement fully electronic mount on lenses, one for the camera and one for the lens. The new version of the mount on the camera would have include everything in the KAF2 mount + support lenses with fully electronic mount. They would still need full support for KAF2 and KAF3 lenses, so screw-drive and mechanical aperture control will still have to be included in cameras.
The version of the mount on lenses will have to remove all moving mechanics in the mount and add support for fully electronic control. So KAF4 for the camera and KAF5 for lenses. But I doubt that KAF5 lenses would be supported by older cameras (KAF2 and earlier).
New lenses certainly would not work on older cameras (which are already impacted by the absence of aperture ring anyway, sadly) but I'm not certain a new lens mount is required (if only for literature) . After all, there's a digital pin already, it may be able to transmit more than it already does (it does more now than in did in Z/MZ serie bodies already). On the body, well... if digital pin is sufficient, same thing but obviously the body should detect if there's a new lens and not actuate the mechanical linkage etc...
Same thing as now: the body does not actuate the screwdrive AF if there's an SDM lens. Rather simple to implement.
Oh, btw, a motor of some sort should be embedded in each lens meaning lenses would be even bigger. So for those who wants all modern lenses à la Canon, keep in mind that:
* AF in the body takes places (and breaks more easily)
* In lens SR takes place and more optical elements (price)
* In lens aperture control takes place.
Don't moan because Pentax lenses would be big... (but fully modern and supposedly better performing, indeed).