I love the Jupyter ecosystem but it's frustratingly messy sometimes. There's already "nbconvert" built in to Jupyter (lab), built on Pandoc. It's extremely under-documented but it's possible to extend it with templates to generate arbitrary outputs. I've done this to directly generate branded PDF reports via latex. Jupyter Book has a lot of overlap with this feature, but rather than building on nbconvert/pandoc, it starts from scratch with Sphinx.
Oh well! Keeps things interesting, I suppose!