I genuinely wouldn't be surprised if opposing Solas at any cost in DA4 will result in him turning into an actual pride demon at the final battle. Given the revelations about spirits & elves being much closer than they once were, I think it's quite possible that the allusions to pride demons - in Solas' name, in the six-eyed depictions of the Dread Wolf - turn out to be literal, rather than just a symbolic discussion about Solas' struggle with his own pride, his greatest asset and his greatest flaw. After all, I think 'opposing Solas at any cost' will likely push both the Inquisitior and Solas down quite a dark path, a race to the bottom as such, so the idea of him being 'corrupted' into a pride demon isn't exactly far fetched.
Interesting. I remember my first gut reaction to Solas, in my first playthrough before I finished the game and found out all this other stuff about Fen'Harel and the ancient elves...was that he was a mage possessed by a pride demon. He mentions befriending pride and desire demons early in the beginning of the game, and ever since I thought there was just something... pride demony about him.
Given the revelations about how ancient elves may have been a lot closer to spirits, and that he says he was Solas before he took on the title of Fen'Harel, I think it's more complicated than that. But his character arc still fits the theme in DA about the quest for justice and freedom having a double edged sword. This theme goes all the way back to Mouse in the mage origin story in DAO. Anybody remember Mouse? Uldred. Then there was Merrill with Audacity and her mirror. Hawke's downfall in Kirkwall. Now Quizzy's impending downfall, potentially.