It seems the G-buffer used in UE4’s deferred rendering needs more information than what is currently allocated. I’m sure sooner or later UE4 will offer it as an alternative option, much in the same way they allow toggling of a normal underneath the clear coat, and the addition of more color information for subsurface scattering materials. Presently, anisotropy has to be simulated by shifting normals of the surface into multiple directions per-pixel to give the illusion that light is spread over the surface. Obviously this illusion is not perfect.