Great idea, but why not just outsource the social aspect and leverage pre-existing link-discussion boards (i.e. HN/Reddit/etc)? As a user, I'm unlikely to want to change both the way I comment, and where my comments go.
On the other hand it should automatically submit the link to my preferred site, e.g. HN, and post my comment, thus creating a new source for comments.
Maybe something like this already exists?