You mentioned readium in one of your comments. I’m curious why you didn’t use the readium spec and corresponding ecosystem. Coming in cold and just glanced at your blog post, and I see you’re using RN. There is a RN package that leverages readium under the hood for ebook reading (I know because I’m the author), don’t know if it’s a weird actually has the api you need.

EDIT: storyteller is super interesting. Dug around a bit in the code and see that you do seem to be using readium for some things, so I must just be missing some nuance.