I Have Kind of the same concern. I am extremely interested in P3Dv4.x for the 64 bit functionality and have been flying FSX and MSFS since First version. As a result I am extremely heavily invested in FSX Add-ons to include my favorites the entire PMDG Boeing line up and Quality Wings 787. Which is an awesome Aircraft by the way. I can only imagine how much better it would be coming from PMDG.
So it sounds like it is not possible to migrate PMDG Aircraft from FSX to P3D, is that correct?