[ UPDATE: looks like someone else already posted this. moderators can delete this topic. thanks! ]
A friend of mine who has made a lot of books with Aperture told me today that he went to print a new book over the weekend and got a message on the screen saying book printing from Aperture is being discontinued in March. One more nail in the Aperture coffin.
On the plus side, he said that books in Photos are pretty flexible, however Photos does NOT import books from Aperture so you will have to recreate your Aperture books from scratch in Photos.