" As a former VP, protocol is that he uses AF2, which he still does as ostensible POTUS"

I never knew that, are you sure that's correct? The status AF1 is the C/S of any of the Presidential aircraft that the POTUS is in at the time, discounting the MARINE1 C/S etc because he's in a Marine Corps aircraft and not the Presidential fleet. I find it strange that the C/S would be effectivly lowered to AF2 when you're actually the POTUS. What would the C/S be of the VP then if they were in separate Presidential aircraft going on different journeys? AF3???