I just dont see a way to make it look nice separating the different addressbooks (and remember, a user may have 15 addressbooks). The list of addresses is a roundcube internal list.js based list object, which allows for a consistent UI experience. I dont think I can make addressbook headers for each addressbook without a huge hassle.
I will remove duplicates, and you'll just have to know if you want to mail george, obama or bill.
Cor