I don’t think this offers anything new on relighting — this is literally just adding the ability to sample a splat during a raytracing render step; nothing about changing a splat’s color / illuminance / whatever. That said, you could turn on, say, reflections for parts of a splat scene subject to whatever rules you wanted.

Maybe you could get relighting here of a sort, by computing some sort of normal to each individual splat as you hit it, and checking light values. That said, the splats don’t (as far as I know) approximate geometry, so normals on them may not be (won’t be?) what you’d expect from actual geometry.

I’d say this would be worth a try, it might turn out to work okay, and would be nearly free in the rendering pipeline they describe.