I fear I might be missing the point here but from a player's perspective I can at least confirm that PMDG 737 NGX with patch level 1c (SP1c) installs and works beautifully under PREPAR3D V2.2 as long as I first install the registry fix that www.fullterrain.com so kindly has made available (see the bottom of their support page and the link to "FSX_Registry_Fix.zip").
I do have the NGO Flightsim Estonia http://www.flightsim.ee/ migration tool installed as well but I have it in "disabled" mode and the PMDG 737 NGX still works perfectly so I am assuming that it is not actually needed to make the combination of PREPA3D 2.2 and PMDG 737 NGX SP1c work.
I do hope this is not in violation of any copyrights or other company rights as the software is being used in a private non-commercial setting albeit the P3D license might be considered "commercial/professional" in some sense and I fully agree that PMDG obviously cannot make an official release that would include condonement from Boeing unless they have their full consent.
Cheers!
/Mats B.