GSX already does exactly that: it removes ALL ground vehicles not belonging to GSX when you activate GSX on a certain gate.
Obviously, it can only remove things that are removable in the first place, that is SimObjects of the Ground Vehicle category. If you have a 3rd party addon that added vehicles or any other extra ground detail as:
- part of the scenery itself as "Library objects", so they cannot just be removed in any way.
- SimObjects with a Category other than Ground Vehicles, so it would be unsafe for GSX try to remove them, since they might be important part of the scenery (like jetways) that should not be touched.
