It's a good idea, but it would almost certainly be a lot of work. The HTC crew would have to go through every aircraft/vehicle (current and future) and decide what to allow, and what not to. For instance, I shouldn't be able to swap from the glass-nose, no bombsight B-25C to the different nosed, bombsight included nose. For fighters, I imagine that switching from 4x.50s in a Pony-D to 6x.50s should be done from the hangar. Etc Etc.
Ultimately, I like the idea for fuel and certain ordinance loadouts. Other extras (adding rocket-rails, things that require more than a "simple" 'sling a bomb to the hardpoints already installed') should be done from the hangar.