The material I've linked to doesn't automatically link back. Instead, I could make a link using his system which includes the text from the version of the document I look at, and provides a two-way link.
It's a nice idea, but unless you can make it easy to create documents with all these links (and ensure they don't need any maintenance) I don't see how it would catch on.
That's the rub.. How do I guarantee that the text I've linked to never changes, nor goes away? I don't want someone changing the content or context of my citations to "rewrite history" as it were, or to sell their own advertisement space inside my website (think iframes), or any one of two dozen different, malicious ways to abuse this mechanism.