I feel like most stories end with a moral, or a character development, or evolution. KOTLC is also, I think going to go the same way.
The Lost Cities (or the elvin world in particular), is already past most of the problems humans face like pollution, gender inequality, race discrimination or global warming. When Sophie first came to the Lost Cities, she thought it to be a perfect world, where everything is peaceful and nothing goes wrong. As the series
progresses, she sees the flaws in the system which will be corrected and presented as the conclusion.
The Lost Cities face challenges such as looking down on the Talentless or 'bad matches'. The entire concept of matchmaking is corrupted. While it could act as a guide, it should in no way be a basis on which to judge a person.
I think that the conclusion of KOTLC will include a world where the matchmaking system is destroyed and Talentless are considered equal. Exilium's name would be changed into something more welcoming and the abilities taught there would be considered more important. Exilium's development has already started by Exile - book 2.
By the end of the series, The Lost Cities will actually be a perfect world, where everyone is treated equally and all the species united and working together.
Humans may still not be a part of this new world, but they will definitely be a part of the novel. As Fintan said in the Peace Summit in Lumenaria, humans are the main challenge faced. It makes sense, and what he said is true. But humans cannot be destroyed, for that would completely be off point. So the end of KOTLC probably features an actually ideal society with harmony all around.
I have more theories about who leads the final battle and where the Council, Black Swan and Neverseen end up, those will be posted in forthcoming blog posts.
PS - thanks to @rakshith23.blogspot.com for helping me with this post!