Can't you just update the P3D GSX with this coding feature for your yearlong followers?
That's exactly how I said it will happen: "Since this is just coding, it will work the same in FSX/P3D as well", there's nothing you'll have to do, the new menu option will just appear, after GSX will be updated for the MSFS release.
Maybe this wasn't entirely clear but, whenever we'll add new features to the MSFS version, if the feature it's just a change in the GSX code and it is supported by FSX/P3D, it will automatically appear there, as a regular update. The codebase is the same, except in places where the two simulators are different in a way that a feature is not possible in one, that's no different than what's happening with P3D 4.5 and 5.0: the GSX is code is basically the same, but it behaves differently in P3D 5, because of the Render To Texture features that require DirectX 11, so they only work with 4.4. In the same way, we'll handle differences between MSFS and FSX/P3D.