I've definitely given thought to the idea of writing a book about Asciidoctor, but I just don't have the cycles I need right now to dedicate time to it.
I don't think the User Manual or Quick Reference are anywhere near ready for publishing, even for print on demand. They need lots of review (for accuracy) and editing.
The first step here is to probably put the PDF generation in place so that we can add a link to the PDF generated by Asciidoctor PDF. That's an open issue.
I still think this is a great idea. But I don't think the time is right yet, at least not for me.
-Dan