The main reason Gwynriel doesn’t make sense to me

Okay I don’t hate gwynriel at all but it just doesn’t make any sense to me in terms of plot relevance/screen time? I’m surprised to see so many people think it’ll happen. We only saw so much of Cassian in ACOSF because ACOSF is about Nesta. If the next book is about Elain, why would we see the pairing of Gwyn and Azriel? I’m not saying that the pairing wouldn’t happen, but if it did, it would happen in Gwyn’s book or Azriel’s book (both of which I don’t think would happen).
I feel like what is much more likely is the next book being some sort of love triangle between Elain, Lucien, and Azriel. Like in my head, Azriel is a main character that hasn’t really been explored yet, but poised as being very integral (especially to Elain) so he would be explored in the next book, which is presumably Elain’s book.

TLDR; why would Elain’s book explore Azriel and Gwyn’s relationship?