One thing I wonder about is what the various goals of structured book review content can be. The classic example would be a citation, to make it precisely clear whence one’s quotes originate and whither to search for context. The second obvious example would be a product review; “should you buy this book?”

Schema.org’s Book schema has some fields that spark ideas, but mostly seems like “bookstore dataset” territory.

It’s the possibilities outside all that that get interesting.