I'm here to tell y'all something.
My HI3rd book will have, at max, probably 6 more chapters.
Now, why is that?
I've done a lot of the things that I wanted to do in that book. The only things left currently in the main part is to bring back the Flamechasers, and the reveal of what came before Past Era Y/N. It will most likely go as: Flamechasers return will be one, there will be another filler, Y/N's full past will be broken up in two, a chapter after that to wrap stuff up, and then possibly an epilogue.
The Honkai won't be defeated at the end. Because let's face it, they were never the focus on this story :P
Though if you WANT to see final Y/N throw hands with the Honkai, we'll see.
This isn't final, since who knows what ideas might decide to show up in my brain, but this is a general outline of what is to come.