A lot of interesting ideas here! The individual book entries appear to be a hybrid of a citation and a review, so I wonder about using microformats2 h-cite and h-review.

On my list of reading posts I use h-cite to mark up the books with the uid being the ISBN or DOI. Check out the parsed result of that page. My list isn’t really a bookshelf since each post has its own read-status, but take a look at the parsed h-cite within each post.

This gets more hypothetical since I have not posted a lot of reviews, but an h-review post could have the item be the book’s h-cite. A bookshelf would then be a stream of h-cite and h-review posts. A nice benefit of that is social readers are already able to subscribe to and display those streams.