True, but since glTF is open format, Blender devs will have a way less pain implementing it. From what I understand, supporting FBX is only the problem because it’s closed source format and because Autodesk deliberately screws Blender over by making small, undocumented changes to FBX with almost every new release.
I bet if UE4 suppored glTF fully, Blender devs would have already provided working add-on for it.