I know multimedia is coming to books. I’ve heard tell of augmented ebooks with videos and sound clips added to them. These are especially useful to textbooks, but not novels. Maps and diagrams would be useful, especially in a convenient pop-up so readers don’t have to flip back to the beginning of the book, but I think there can be one better.
Books with soundtracks. I recently went on a binge of Cowboy Bebop again, and I was struck by how instrumental (pun intended) the music was to the emotions of the story. How cool would it be if every book came with a recommended soundtrack for the book? With a little extra coding, soundtracks could be triggered to change automatically with specific chapters, or even specific page numbers.
Seriously, someone needs to get on this.