In my dreams, the major link aggregators like reddit, HN, and Facebook distill a crowd-sourced abstract for every article making the rounds on social networks (rather than just compiling loose comments). Then a browser plugin shows them alongside the article.
Not sure what you mean. In the sense that it features user-submitted summaries for links, yes. But there are lots of blogs where each post is a selected link with some sort of background info. (E.g., Marginal Revolution also has this format for many links.) My dream is to have this for all sufficiently popular links going around the internet on a given day, and to let the summary get progressively more refined.