I don't see anyone saying safety or ethics, so I'll just put it out there that it has some safety and ethical considerations you should consider.
Consider "inflammatory" books and how they could be used to harm a group of people. Although I recognize folks post this "publicly", I think the intersection feature provides more than Goodreads.
Let's say, people who have read "Mein Kampf" & "The Anarchists Cookbook" or some other combination that say "Antifa" to the current regime.
I'd recommend you have a list that you consider private, always and allow Users to add to that list so it's more scalable. If folks try to intersect with anything in that list, you can warn that you don't allow intersection with private books.
Anyway, super fun demo!