For what I saw in
www.cefathecat.com (I like the books, good job) I would say it is totally possible. BUT keep in mind that App Inventor is not really a professional or full featured programming platform. It's actually a learning tool that exceeds its purpose. That's why a lot of people feel like it's limited.
So, if you start doing one of your animated books, you may feel at some point, that the limitations are too big to keep going, but if you keep the graphics and sounds low in size and an optimized use of the blocks , I don't see why you shouldn't be able to make a good animated book.
Good luck with that.