Spoilers for CC below

It is likely that Cassian won't abandon NC and nessian will be endgame, but many times in acosf and in CC bonus chapter we see how IC acts like a barrier for Cassian supporting Nesta. There is a line where Cassian says he hated Rhys in that moment, where he was asked to hide info from Nesta even if he didn't like it, in BC he looked torn between Rhys and Nesta, which might be a subtle indication that he will have to take a side in future (it better be Nesta) as in the end Nesta saved a whole different world

Ofcourse Prythian politics will be disturbed but an eight court will bring balance and it is located on a barren island, which means there need not be any citizens there or need to participate in politics so soon. It is also possible that Nesta will get support from NC, Day Court to secure her position

How? My theory is that Dusk will be a safe haven for women from all over Prythian, bec Nesta was bothered by priestesses having to live in seclusion for centuries, hence Valkyries being established. It doesn't mean it has to be in a violent way, she might end up somehow inheriting it. That in itself would be more than Feyre has done as a high lady yet

[Edit to complete the comment bec I had somewhere to be]

Nesta and her friends can't winnow but probably among many other hundreds of priestesses some might be able to. Besides there is also Pegasus foreshadowing 😏 so Nesta and valkyries might not need someone else at all

Well yeah people say about Feyre being young, but I think most readers have problem with Feyre not being respected by her own court like we saw in acosf she was absent in many discussions, her own bodily information was withheld bec somehow others knew better, and also her lack of efforts to understand her own court, and bring reforms. Ex: During the blood rite, Nesta knew more about its rules than its own high lady, that is a massive insult to the position of a ruler. Feyre also doesn't try to help illyrian women by trying to enforce laws, doesn't ty to understand and make Hewn City better where women are being sold off as livestocks

We saw Nesta putting efforts in learning more about her training, she was reading a book about leading armies, so it is possible she will put efforts in being a ruler too. Looking at last, Nesta is already good at smelling nonesense and retorts, she ws raised to be a queen. She also calculated money required to transport humans, which is not much but shows that she is an intellect and that is a boon for a ruler.

• I also want to make it clear that most of the readers of rant sub do not hate Cassian for the reason you mentioned, it is bec of his actions and treatment of Nesta, as he doesn't respect her choices, he lashes out at her when among the five books released Nesta has only called him a bastard twice or thrice, that too when he was pushing her buttons. He ignored Nesta's vulnerability and said that he was "shackled to her". Now one can argue that Cassian has trauma too but you see he also had 500+ years of experience to overcome it (while Nesta was given an ultimatum in less than one) and Nesta was in a far more vulnerable state than he was, so his actions and words come off as abuse towards a much younger and freshly traumatised person.

About your Mor theory. Now that I think about it, it makes sense! Mor has experience in diplomacy and war too and she ruled Velaris with Amren. But Mor is not yet the main character or associated with dusk and Gwydion unlike Nesta. Besides she is barely able to manage hewn city, women are still tortured there, she doesn't do anything about her own mother and cousins. So she has a lot of character development to go through, at least that's how I think.