I've restructured the plugin SDK for our new engine and created a new repository on Github here:
The GMF2 format will only be used as an internal data transfer protocol for model loader plugins. Our main supported file format will be GLTF.
As of now, the plugin system can be used to write texture loaders for different file formats, model loaders, or to modify behavior of particles in the new particle system. The FreeImage texture loader has been moved out of the core engine and into a plugin so you no longer have to include the FreeImage DLL unless you want to use it. The main supported texture format will be DDS, but the FreeImage plugin supports many common image file formats.