There is a feature that would make me very happy man: the administrator could turn on an option so that when anyone creates a child page in a book it will, by default, inherit the taxonomy of the parent page.

Comments

That's what I'm looking for too

The same here guys.
I am just not sure if this should be a taxonomy or book module issue.
I have opened a ticket in book queue. So far no feedback, feel free to drop a line to shake up the issue => #1574734: Child page auto-inherits parent taxonomy .