Only problem in that theory is that Flightbeam's KMSP doesn't use the FSDreamteam Add-on Manager, as Flightbeam created their own with that one.
The FSDT Addon Manager or any other addon manager doesn't have anything to do with the usage of the official add-on installation guidelines from the P3D SDK, which anyone can choose to follow or not, regardless how the scenery is made.
As I've said, the problem is that every utility that must read the scenery library for any reason, in order to claim to be fully compatible with P3D MUST be updated to include scenery areas added with the add-on.xml method, because reading the scenery.cfg is no longer enough to have a complete list of active scenery areas.
These guidelines has been out since P3D V3 was released, so developers had about 2 years to prepare.