There is a "Sphere mask"- node in the Unreal- material editor, which you can use to have a spherical gradient texture tracked to the position of the object but always facing the camera and ignoring the normals of the object. I want to do the same in Blender.
So, basically the effect in the linked image. Here i used a mapping node to manually move and scale the gradient to match the monkey, but if i move the camera or the monkey the gradient of course does not follow.
Any way of having the gradient always be centered on the object?