I had a quick look a the glTFLoader
source code and it seems it loads only textures which are bind to a material.
However you could create a dummy material and try:
BABYLON.SceneLoader.OnPluginActivatedObservable.add((plugin) => {
plugin.loadAllMaterials = true;
});
this should load the material even if it’s not assigned to the mesh.
I believe loadAllTextures
property would be handy as well.