Would you think a book recommendation would be a great idea, or not?
Book recommendation questions have a tendency to invite multiple subjective answers and fall under the "primarily opinion-based" close reason which applies on all sites:
Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise.
Furthermore, we can learn from the experience of previous incarnations of the Literature proposal. Quoting from this answer from 2011, relating to an older proposal then named Books and later renamed to Literature:
One thing that worries me about the book proposal is that three of the example questions are book recommendations. We tried that on SF&F, and after a while we weren't so hot about them, because most recommendation questions were pretty bad (the questions were usually too broad, and the answers weren't very useful because they rarely explained why the answerer thought the proposed book was a good fit). [Ra'T note: recommendation questions are now banned on SFF, and have been for many years.]
And a comment on that same answer from a member of that failed incarnation of Literature:
I'm not a mod, just a member of the Literature site. Guess what: The recommendation requests ARE a nightmare. They are relentless, numerous, and often very obscure or specific. I have no solution to propose.
This is almost exactly the point of the example questions: testing the scope of the proposal and demonstrating what the proposal is about and not about. If you want to know whether something would be considered on-topic or off-topic, propose it as an example question.