Okay before I get to the real story, there's going to be three Daring Do novels, which will apparently be sold together as a set and come with a with a little golden idol daring do figure. Call me surprised, but not really caring. Yeah I'll probably read them, but I'd have rather read about literally any other character in the entire series.
Now the real news. You remember back in Castle-mania, when Twilight found Celestia and Luna's childhood diary. Well it's going to become and actual book. As in, we're going to get a book that discusses what Celestia and Luna were like as foals. Now before anyone get's excited, I know I am, I'm going to temper it with, it's probably not going to be what we want. It'll probably just be stuff like "Boy I really like the secret slide" or "Big sis Celestia sure does eat a lot of cake" type stuff, and not any real information or lore building. But, I would be happy to be proven wrong.