PBR lighting; Transmissiveness; 3D model improvements & more.
So I guess instead of allowing us to do lighting in effects, you'd rather add a new Material addon type, which has access to lights, normals (maybe even the vertex shader and additional textures for normal maps for example). This way it would always be the first shader and could sidestep the awkwardness with effect stacking, where only the first effect can do certain things.
That indeed would be more complex to add, but also sounds more robust.