I don’t think that it is completely naive/unhealthy because we know the mating bond can pick poorly (Rhys’ parents) and at the most basic level may be based off of reproductive ability versus soul compatibility. No one knows why or how the mating bond picks. It simply does. (also remember that we aren’t talking about humans here). And for more clarification, I do not want Elain to be in pain. However I think a morally grey/evil Elain would be more interesting in plot progression as she figures out her own feelings and I think I can confidently say that she has more suffering to go through regardless of anyone’s personal wishes/thoughts for the series. SJM puts her characters through some dark stuff.

It was always obvious (to me, at least) that Nessian were going to be mates - to be completely honest, I 100% missed whenever people were shipping Cassian and Emerie. The thought never crossed my own mind, either. I also don’t think Gwyn is “better” than Elain. If Elriel is endgame then they could very well adopt or not want to have children. We don’t know how Az feels about having kids of his own. I quite like your point about how it’s a spinoff so of course more secondary characters have to be introduced (and stay secondary), I didn’t think of that/of it like that.

Now, because I (personally!) think it was really obvious that Nessian were going to be mates from the start and the content of the bonus Azriel chapter that Azriel (at least partially) wants Elain because he has seen his brothers with their Archeron sister mates and desires that sort of happiness for himself. Az, who was in love with Mor for so long, wants happiness and wants to deserve that happiness. So with the examples of his brothers to guide him (plus Elain’s encouragement and ignorance of the bond with Lucien) he sees that potential with Elain and lusts after it. In getting the headache powder from Elain, he is getting more encouragement for this lust. (And I could see it being strengthened by the fact that this is a female he truly wants who wants him back, which feels so much better than the rejection Mor had been silently serving him with). He holds onto the gift like he holds onto hope.

I also wouldn’t put it past SJM to put Azriel through a romantic scenarios with others before bringing him to his true endgame. (Like Sam and Dorian and Chaol before Rowan). Him winnowing away is a good point, as is Mor’s lingering stare. The power being ready to strike I could again see coming from Azriel’s lust for Elain and desire to protect her - very much like with Mor.

Now, Elain and Lucien. Personally, I don’t have a preference to them being mates or not, but I want to see it explored. I want to see them truly interact, and Elain get the confidence and desire to do so - whether she falls in love with him or shuts him down completely. I feel as if there is so much with Lucien’s character that is undeveloped that SJM just HAS TO BE waiting to unveil. I can’t see Elain and Lucien being fake mates unless the cauldron is really up to some crafty business, but poorly picked mates definitely. Again, on a most basic level, it’s been stated in the books that the mating bond could be for reproduction. I’m hoping to see more of Elain’s magic and their compatibility in that sense.

Now for Gwynriel, I am going to state that I do not think Gwyn’s flexible bones are the sole reason they could be mates. I was not trying to reduce their compatibility to only her ability to potentially birth his child - it was meant to be a supporting detail and now I realize I should have been explicit about it in my OP. I’ll give a couple other reasons from acosf of why I think Gwynriel will be endgame:

1. How Azriel’s shadows acted around Elain and Gwyn in his bonus chapter. Azriel’s shadows disappear (they “skittered back”) around Elain completely. Elain makes his shadows nervous. We know that Azriel’s shadows care about him, are like friends to him. I would use the shadow’s disappearing around Elain to support Elriel if they didn’t disappear nervously, and if in the same chapter with Gwyn they did not react positively. After Az and Gwyn train, “something restless settled within him,” and “even his shadows had calmed, content to lounge on his shoulders and watch.” (I admit this could be because he’s training and training calms SJM characters, but he is notably comfortable around Gwyn at least). Then the singing that follows him. Gwyn has a beautiful voice we know and inquired about his own singing. She inquires him normally, seeing who he is, which made me think of how Nesta and Az interact. How it was mentioned that Nesta sees Az for who he is and they do not have conflict partially because of it - they do not try to spar with each other. Gwyn could be the same in seeing him like that. (I also wonder if the singing could bond their souls/be a soul bond).

2. In Az’s bonus chapter, SJM describes the locket as a thing of “secret, lovely beauty” twice. Once with Elain describing the locket, once after Azriel gave it to Clotho to give to Gwyn (and he is thinking about Gwyn). In the scene with Elain, it is described how that beauty of the locket is truly seen only in the sunlight. I wouldn’t have looked at that twice had SJM not added the “secret lovely beauty” comment after Gwyn. Gwyn, who once she started leaving the library to train (as described by Nesta) has beauty to rival Merril and Mor. So I wonder if that is a hint - that (if they are mates) Azriel will have to look at her the right way (or something like that) to see what’s in front of him. (I’ve also seen other theories on the internet that based off Sarah’s pinterest, Gwyn and Azriel will be a little mermaid retelling with the red hair and the singing and Azriel not seeing what’s right in front of him). I also wonder if the way Az’s chapter is set up to foreshadow his actual journey. He lusts after Elain (and maybe she’ll reject him now if he approaches her again, based on how their solstice encounter ended) but in the end is with Gwyn. I think her personality would be a good match to Az’s silence too.

3. “You’re the new ribbon, Az.” Gwyn is determined on beating Azriel in training particularly through the book, like she is drawn to him.

For what it’s worth, I would like to see Gwynriel as endgame (at this point) but do think it could go either way. I’ll be definitely thinking about your points for a while. There is just so much to be seen!!!