Interesting... if this works the way they designed it to (or, for the more cynical out there, "the way they claim they designed it to"), it'll shift SEO away from Google-bombing / keyword bombing and towards producing quality content. On the other hand, depending on how it quite works, it might end up just replacing the bomb site results with "most engaging" sites, which could be considered a net negative result, since I think we've all learned in recent years that engagement metrics are a poor substitute for quality metrics.