It's not super difficult to take Jekyll-ish input and generate books from it either, e.g. I built a tool to do this:
Example of a book I published with this approach: https://www.amazon.com/dp/0692553916 (a fairly challenging type setting problem with lots of footnotes, foreign language, etc.)
The main gotchas are that if you really want it to look good you have to dig into the Latex template, so ultimately it would take more effort to make it push-button for non-technical users.
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