Cargo pod doesn't need to be huge IMO, that will only delay the deployment of the troops even more, which nobody likes (why do you think many maps have the spawn points out of the dropship in the first place).
If you really are that worried about manoeuvring inside the pod, let's say that the seats fold against the wall, and voila lots of space to manoeuvre with no need to change the floor plan (except for UGVs, but that would require a ridiculous size, don't even think about that).
Also we haven't discussed all the different models that are needed to add a single aircraft to the game (geoscape model, UI models, several battlescape models...), which we probably should do soon.