Safari and autodetection of RSS feeds

This is something that sounds hackable at the least.  Brent, could
something like this be done with WebKit's tools (asking out of

What if Safari detected RSS feeds?.
Here's an idea for Safari: Many web sites/pages now offer an RSS feed
equivalent of their contents, not unlike this weblog! As RSS is getting
more and more popular, it would be cool if Safari would detect the
presence of an RSS feed (through the tag) and activate a UI element on its toolbar that the user could use to drag to their favorite news reading program …. Say, NetNewsWire.

mockup of Safari toolbar with an RSS item [Karelia Software]