> I would love it if paywalled/registration required sites would get downweighted so as to encourage a discussion of the article.

That's only a problem when these sites get posted a lot.

Counterpoint: The London Review of Books had a few front page appearances here, it is a site posted quite seldom, it has spectacular articles, and because it's posted so rarely, pretty much everyone who clicks on it will still be within his number of "free articles".