I thought about it while writing this post. It would be useful to have a decay factor for PageRank. In simple words, if someone wants to maintain their PR score, they need to actively engage in the HN community.
Wouldn't that encourage people to "actively engage" even when they have nothing to say just to keep their score?
Goodhart's law comes into mind here. People who want to stay relevant on this site will take your measure as their target. There's no system that can't be gamed if you know the rules. But the more "rock solid" you try to make those rules, the more you embed intrinsic discrimination between participants. You put "Proof of Work" in the rules and you alienate newcomers while all the rest do "busywork".
Your own comments and submissions would sink like a stone because you didn't engage enough, regardless of how interesting your points are.
> Will I ever publicly write about how HN ranks posts if I am Dang (HN moderator)? No, because Pagerank can be manipulated by people despite its reputation. In fact, Pagerank is being exploited for years. Moreover, there are financial incentives for companies to get on the first page in HN.
Lack of transparency is not a solution, and certainly not one that will sell well in a place where "security by obscurity" is disdained and open source cherished. It's particularly bad when you're dealing with a high profile site filled with intelligent people who would most likely make short work of reverse engineering just enough of the algorithm to understand how it works.