tedster - 6:58 pm on Jun 28, 2011 (gmt 0)
Here's my speculation. I think there's already a section of scoring in the algorithm we could call "engagement".
We've already been talking about many of the factors that could go into that score. I could be a complex combination of social media, contact information of various types, newsletters, RSS feeds... on and on. All the ways that a website actually gets involved with their visitors.
The final, aggregated engagement score would be combined with relevance, PR and "quality" scores. A site would not need to show ALL the signs - a well read newsletter but no RSS feed? You're still showing engagement.