I dont know if this game engine can take it, but I think this game could fair extremly well with a pvp or multiplayer aspect.
it would certainly boost its online presence boosting sales.

It doesnt seem to complicated from a superficial perspective.
However I cannot get over how cool it would be a to see different and diverse planes go head to head in a competitive aspect.

co-op
1v1
2v2

Maybe even just a free roam.

Personaly I feel like there should be no balancing / xp system. just a user leaderboard / design leader board.
Alow the comunity to desingn and test planes preformance and see how they evolve amongst the comunity.

If anyone knows more about programing amongst the comunity it could be built as a mod and shown to the devs.
Since I've discovered this game I've loved the concept.

It has so much potential to be a truely awsome game with a huge fanbase.