Well, I think it would be weird. I wouldn’t hate it… But I also feel like it doesn’t quite answer all the questions. Is she a Light Lord? Is she a Void Lord who somehow has some kind reign over the Light? Why does Xal’atath call her the “Upstart” Goddess?
I have no real issues with that theory, I just think it would require a bit more refinement, and doesn’t quite fit as well as a Life and Death Deity.