Merging Word Processing with Music Notation isn’t a niche thing. Away from all the scores and parts, there are thousands of textbooks out there that mix the two together. Most of them are hundreds of pages long. Some of them are centuries old. And as far as I know, all of them organise themselves into chapters - that’s their way of defining “independence” within their work.
BUT…
Using the criterion of independence for both genres exposes a philosophical and semantic incompatibility between a musical project and a text project. If a musical Flow in Dorico is defined as an independent piece of music, and a textual flow is defined as a chapter, then any work which comprises text separated by music or music separated by text is actually a mixture of two different types of flow which will fight each for supremacy.
David