Not really sure if this might help with your issue but if you check this topic there is a standalone GLTF Viewer, attached at the bottom of the post and currently using r168, which will allow you to manipulate any parts of the code so you can see the outcome.
In this viewer I went about replacing all applicable materials to node materials - if you do a search for node_materials in the code then you could see where they are used.
GLTF models appear to load and look properly, to me at least.
EDIT: Just updated that viewer to handle VRM files differently and also for materials to cast and receive shadows.