Gltf has now been around for a while, and is much better defined than the currently supported obj, stl and fbx formats.
Are there plans to support it in the Mixamo website/auto-rigger?
plan is a strong word
yes Gltf has been around for a long, Long, LONG while... which is why most people stopped using them
Yeah great response!! I totally love converting everything--and I mean literally EVERYTHING into fbx before adding animations to it and then losing all of the materials afterwards and having to add them back in Blender! That's awesome. But apparently GLTF has been around a while so therefore there's no need to support it!!!