Ah okay, at least PMDG allows that Level of Integration with GSX^^
It's not a matter of PMDG "allowing" things or not, it's more like GSX, by design, is made NOT TO TOUCH any systems on the airplane.
Meaning, it won't ever write on any variables on any of the plane systems, that's why we never made an automatic door opening system, because we can't possibly be sure if it's safe to "just" open a door when it might be tied to a custom system, for example the electrical system or the hydraulic system. The one and only time GSX ever changes some variables on the airplane, is during Pushback, otherwise it wouldn't be able to...move the airplane. But this is done using entirely official documented variables, so it's not as if we are touching a custom system.
Same for fuel: we only refuel ( acting on fuel quantities ) planes that are known to use a standard fuel system, otherwise GSX will only do animations in reaction to the changing fuel levels which are already happening under the airplane own control.
Same for the battery charger or the external power availability, we only charge the battery for planes that has been flagged to be using the default electrical system, but most of the 3rd party planes aren't, so we just signal developers using GSX-specific variables that we would like to charge the batter or a jetway has power or air, and then it's left to the plane developer what to do with this information.
That's the only way to be sure GSX will never mess up with any airplane system that might have repercussions we cannot possibly be aware of, and that's why we ask plane developers to do some bits of integration themselves, because nobody better than them can possibly know when it's safe to act on their own system.
Some major plane developers ( FS Labs, Aerosoft, Leonardo ) fully understood this, so they did the integration themselves, since they obviously saw the value GSX added to their customers.
The one and only exception is PMDG, their explanation for not integrating it was they fear "GSX would mess the airplane", which is precisely the opposite of why they were supposed to do the integration themselves.
If GSX really tried to mess with the airplane, there would be no need for us to wait for plane developers to integrate anything, we could *hack* into the airplane ourselves (like we used to hack into FSX own memory when the SDK was missing features, but we don't do that in P3D) and could start setting stuff on our own and THAT would be a legitimate cause of concern for airplane developers, which would be unsustainable for us as well, since we'll likely have to keep our code updated with every release of the airplane.