I'm not sure this is going to come out in any way that's legible as an actual point, but here goes:
I'm so sick and tired of "has to" when it comes to the next ACOTAR book(s).
When it comes to a fiction series, the only thing a book really has to do is move the plot forward and do so in a way that makes internal sense (to the universe as set up previously). There are other elements attached to this, like character development, subplots, individual arcs, etc, but that's like...bare minimum. We can extrapolate what MAY come of previous setups, we can have personal preference regarding what would make the story good, but neither of those things have any actual bearing on the story the author decides to tell.
There are very few things that the next book "has to" do, in reality. I'd argue that the only things it has to do are:
Resolve Elain's mating bond situation
Move the queen/war/Koschei plotline forward
Both of those things have to make sense INTERNALLY. To the world of the characters. That's it.
Everything else, including the details and the outcomes of those two points, are theory. Some theories are more well-connected to the established plot threads than others, but they're all still theories.
The next book does not "have to" be Nesta's POV or multi-POV because Bryce gave Gwydion to Nesta. There are a lot of potential outcomes from Gwydion being in Prythian at all, being given to Nesta, etc.
Neither Elain nor Nesta "have to" be the ruler of the Dusk Court. We don't even know that there will for sure be rulers of the courts by the end of the series.
Random side characters you, personally, have taken an in-depth interest in do not "have to" have their stories told in-depth on page.
We do not "have to" get the POV of every single character in order to expand the world we've seen so far, we just need a main character whose plot doesn't necessitate staying in one place most of the time.
Yes, SJM could theoretically "do anything," but realistically she's set up plot threads for a reason. She's going to use those to develop the story further. Some of it will likely fall in line with text-based theories, some of it may not. Some of it may seem to and then take a twist nobody expected. But all of it will have to make internal sense to the universe and to the story SJM is telling. There are a lot of ways to tell a story.
(And this isn't even getting into the fact that we don't really know her plans for the expanded universe beyond the end of the spinoff series. She could very well be establishing plot threads for characters whose stories have been told in this series to have expanded plotlines in books further down the road. A hint to something does not necessarily mean that needs to play out on page immediately.)
