I love the Web Annotation specification. Comment on anything on the web! Share those annotations! And it will let you select/target content in the page. But actually being able to annotate something like the discrete comments within the page, that feels missing.

Maybe good reads lets us view a specific comment by a specific author: there's a page for it. That we can annotate & mark up, in a way we can aggregate against that comment or that author. But if we're just browsing a list of reviews, there's a missing link in figuring out semantically what it is on the page we're trying to markup.