It could be done, certain passages could trigger a song. You could have it loop until they reached the next change, which could get annoying, or just fade as it comes to an end and pick up again when you hit the next track. That would be very cool. It could be an optional additional purchase, sound track for a couple extra bucks. I have a few books I would do that for. Especially the Kitty Norville books which the author actually has a playlist for at the beginning of the book.