What would the spiritual successor be? I personally really liked the story of Ouroboros and would have loved to learn more about the setting, because it was really good how you integrated the whole timeline reset mechanic into the story.
I personally wished there were other people I could have saved, beyond immediate love interests. I got really drawn into it.
Also if a direct sequel gets made, I think that Atreyan taking over the body of the custodian or going through the custodian's memories would have been interesting. He learns about the state of the outside world, and plots on how to turn the tables on his captors.