Books make up for over 200 spots in a house. If one wanted to make a library, they would have to sacrifice a huge portion of their furnishing limit (I own the Daggerfall outlook, so that'd be over 2/7 of space with ESO+....and that's at a house with the MOST spots.) If the houses are going to be limited to 700 items or less, can a separate category be made for books (similar to the separate Trophies category)?
Another option would be to allow us to extend beyond 700 furnishings (or whatever your house limit is.) This would be amazing too!! But I do not believe 700 spots is enough for even the biggest house. With the amount of furnishings now available, one would want to extend beyond 1000+ spots.