First of all, thanks for taking the time to read!
In terms of applying this process to fiction, you could still break the overall book down into chapters, sections, characters, etc. in order to get initial feedback from potential readers.
I actually did this with a fictional web series I’m working on called “Coworking.” The point of the series is to share the random and ridiculous experiences that happen while working at a coworking center. I decided to test the series by writing a post called “People You Meet @ Coworking Centers.” It focuses on the potential characters for the series.
Hopefully this helps! Thanks again!