If you’ll indulge me, I strongly suspect that a potential endgame here is Sebastien as a sort of radiant king, and Siobhan as a sort of night queen.
One of the ways I see this signaled was the Radiant Angel’s success in the fight Sebastien staged on the element fights she did as an exhibition.
But also the radiant Gestura magic Sebastien uses. I suspect fellow students have watched her do it, so there is a story there that people can tell about Sebastien.
I feel like followers of Sebastien get the Gestura magic, and the Followers of the Raven Queen get something else - something more obscure (like some sort of dream Shamanism)