Totally agree, Dubious - it's not really needed. Just a minor wish. It just surprised me one day looking in the back of my M3 and seeing the empty view, and it's been in the back of my mind since then. Today I mashed up some screenshots to illustrate what I had in mind.
My answer to why I'd want to see them is because if I loaded them in the hangar, it seems like they
should be present in any views where they would appear - not unlike expecting to see bombs or drop tanks hanging off your aircraft's wing hard-points, if you had selected them in the hangar. I'm not sure what the game design term for that concept is - logical continuity?
I've also seen empty M3s speeding along from ambush vantage points and have been curious to know whether troops or vehicle supplies were being carried. Many (most?) times its obvious by the direction of travel and who owns the town, but the extra detail would still be cool if the change didn't impact frame rates or production schedules too much.
Wanting German uniformed troops in the SdKfz could just be mild OCD.

I'm a big fan of the idea of parked aircraft also, and agree completely about the added value to advertising/filming.

EDIT: A correction to my first post- if you carry the 75mm gun, the rear view shows the gun mount/base, not the empty view of the back end.