When editing a scene manually you can set a pbr material to either specular or metalness. All materials in a single scene use the same type. If you switch one material from specular to metalness all materials will switch with it.
When editing a scene through the viewer API it's possible to use both material schemes in the same scene. This is great because some materials look better in metalness and others in specular.
I'm wondering if this is a loophole which will be closed soon or if this is allowed. My scenes look a lot better when having both material types in the same scene.