Is this what digital has over paper? Yes. Probably. Maybe. I was reading Miss Peregrine's Home For Peculiar Children (got stalled) and that's illustrated with vintage photos. It's not unheard of that a paper book for adults has illustrations. Tolkien's books have maps.
But, come on, that's not really what we're talking about--a family tree or a map or even a recipe. We're talking about illustrations. I wish I was talking about video but that's beyond my capabilities. My multipli-talented friend, Michal Towber, wrote a wonderful novel called Witch and did the soundtrack for it. That should be in there. There should be a way to play the song/music at key points in the story. I don't have the programming knowledge to do that but someone surely does.
And don't say illustrations are reserved for children's digital books. Some of my adult books are illustrated. Yes, it's true they're romantic comedies. But my friend, Chris Westphal, wrote Inhuman, and created 150 illustrations to go with that and it's a police/psychiatrist forensic procedural.
As a thought for the New Year, think of ways to add content. Even if it's an author interview, or a short piece on some aspect of the story, consider including it.