Export basic properties from other material workflows

[pyaggi]

I'm working on a game engine where people could eventually upload assets. When models are cooked with
a different material workflow than 'Principled BSDF' they loose all their properties, that becomes a very frustrating experience
that can not be resolved from the engine point of view.

I would like the exporter to provide at least the very basic info, like Base Color. I think that way it will provide a basic 'usable' experience that will not discourage users so easily.

I think that will be very useful even in development procedure, where assets from different sources become more 'usable' for testing.

[julienduroure]

glTF specification is based on PBR materials, aka Principled BSDF.
For any other workflow, we unfortunately can't manage every single case.
I think the best way to go is use extension addon with gather_material_pbr_metallic_roughness_hook in order to manage your own rules about material export