Following this technical post, the 2 additional pins seems related to lens identification only (rather strangely I would say).Well, on EOS M and first EOS R there is no in camera stabilisation for photography, only for video. So I guess that's the subject here.
The EF lens mount
Maybe because of the collapsible design with the in-lens barrel swich (11-22 and 15-45)? The body display an error if you turn the camera on with those lenses retracted.