We announced multiple times that we'll continue to support P3D with our most important product, that is GSX, because it's a product that has been designed to be cross-platform and, regardless how much the P3D market has shrunk, it's still viable for something like GSX.
About airports, we are in pause right now, because we simply don't have the resources to support more than one simulator at the time and, there are enough major differences between P3D and MSFS that impact airport development so much, that is simply not feasible right now to support both, and the more the MSFS SDK progresses, the more we learn and the more we use more and more MSFS-specific features, the more complex becomes to support FSX or P3D as well.
However, there's a huge difference between dropping support for FS9 ( in favor of FSX ), which we did in 2011, or dropping support for FSX ( in favor of P3D ), which we did in 2017, and it's the older simulators didn't had any future, because their were unsupported for years. P3D is still in active development, so it's possible future versions might improve the graphic engine and the way airports are done, possibly making it easier to do an airport which could run on both with minimal changes, so we could resume airport development for P3D at any time.
But as I've said, P3D support for our main product ( GSX ) is not going anywhere, and we are close to release a major ( and free ) update to GSX, specific for P3D, and it will be out way before the eventual release for MSFS.
