Worldcoords-XY is just way to tile a texture using worldcoords from top down. It would cause the noise pattern to stay constant in the world so if the sphere moves, you’d see different parts of the texture:
Could just as easily use default UVs for the noise texture (by just not connecting anything or using a texturecoordinate node with any tiling). I was just giving options.
Using second depthfade with sharper gradient for the outer edge:
Only have to do 1-x on the inner gradient.