Thank you, I finally got to see what is up at ~7 to 8 o'clock on the front end of the FTZ! I gather this switch is what prevents a non-Ai lens from being OK.
If you look carefully, you can see the switch is pushed in when the lens is set to minimum aperture. That means pre-AI lenses can be mounted, the greater overhang of the aperture ring will simply push the switch in regardless of the aperture setting. This is similar to many of the low-end DSLRs. It means most pre-AI lenses will probably mount with no problem (it would be nice to have this confirmed though).
Also, on Ric's demonstration, we see the lens stops down immediately when the aperture ring is turned, so stop-down metering is employed and you get "full-time" DOF preview. If the aperture stop-down lever in the FTZ adaptor had been engaged, the lens aperture would be held open regardless of the aperture ring setting, the lens would only stop down at the moment the picture was taken. The camera of course has no way of knowing what aperture is set, so the exposures would be wrong. Therefore, the aperture stop-down lever is somehow not engaged when non-CPU lenses are used. It would be interesting to see how it works in more detail. In a few weeks I will be in London and hope to visit Greys of Westminster, hopefully I will see for myself