If I understand your point correctly, every sub-category in Plane here Are very different areas of expertise.
I agree with you that they could be designed in a pluggable manner.
But here is where you loose me: with the License issue: Lets say every author differs on their opinion of what license to give any given of those units. We end up with the scheme

1. Under what license can we offer the plane in the sense of that plane being an installable unit?
2. If we allow the user/player/developer to say what license he is willing to accept, and say he wants the GPL content? He could get the config, the 2d and the effects. Is he getting something useable by all means?
mix and match licenses is an standing problem in the software world. If we think of it as a functional unit, then that I think would be the plane, and whatever license covers the whole work one has to agree that the whole plane should be obtainable in a way that operates. So, saying FDM-guy, you make your FDM package and you fully control from distribution to licensing at your way, effectively limits that FDM to be implanted and redistributed with other content, unless the FDM author is on agreement with same licensing rules.
Licensing nightmare continues:
One could produce, lets say a CC-NC-SA fdm and a propietary payware sound package that plugs in nicely in a plane that every other component is GPL. Clearly, if the system is plug-and-play enough, then implating/installing that sound and FDM packages does not need to be technically challenging. May be as simple as copying a folder in the aircraft and then having a launcher of the aircraft that allows for selecting sound package (just as changing liveries). Fine. But then comes the problem of effective isolation. You would need to make clear that in spite you are copying the content in the GPL aircraft for your use, now that act has consequences of the licensing of your copy of your plane. Initially it was all GPL and now its not. So, per example, you could have been ok with modify it a little, and sell it somewhere. The GPL let you do that. But now, your Sound that you imported hasnt such Commercial provisions. What do you do? Abandon the permissions that the rest of that plane gave you in the first place? Or risk entering in licensing issues and violations of the sort?
So, again, I dont disagree with you Bomber that a plane is modular enough and that every sub-area of development brings diverse skills, but I dont know exactly what you mean with "the developer of each part gets to pick and choose their rules of the licensing and that prevails over its section of the work".
That works if you don't offer "planes" but if you offer plane-parts and a person obtaining a copy mixing and matching on their machine. And hoping that this person is aware of the restrictions impossed by choosing every single subunit of work.
So that's where I am not following your idea.