You must understand the ceiling height, alone, is not enough to automatically have passengers being able to enter any airplane. It's surely a preparation to extend GSX in the future to work better with GA/Business airplanes, so we added new data like the individual passenger height, the door's height and the airplane ceiling.
However, right now, passengers only have ONE duck animation, which is not eccessive, and it's exactly right for the taller characters to duck to enter the typical airliner door.
To really support smaller airplanes, we would need to add extra lower duck animations to the taller characters, and duck animation to the one that currently don't have one, because they are not tall enough to require a duck animation on the typical airliner door/ceilings.
So yes, everything will come, but it's not there yet.