It would be nice if propellers had a procedural "include swashplate" toggle. This would make building realistic helicopters possible. Right now the only rotorcraft that work in a realistic way are quadcopters, which means we can't really replicate the Ingenuity helicopter in the game, which feels like a missed opportunity.
It would also be so nice to be able to make an autogyro rotor with only onecpart instead of like, 15