Yessss... a library! I love that idea. Basically no games have that unless you build it yourself, and then it's usually not very organized.
After you upgrade your homestead to a certain point, there's a library, and every book you've read is added to it - except for some special books usually associated with quests. Even books you read from before finding the homestead.
To keep things simple, the keyword system would be very useful there:
With as many subdivisions as are needed, until there's an alphabetical list of titles. You wouldn't be able to take them with you, though (so you couldn't sell books infinitely).
Oh, related, I'd also like the ability to read books without picking them up. I missed that in Divinity 2.
