Re demetricating: I've only been on HN for a few years, so I don't know much about its UI's history. But since it's also partially demetricated (not showing votes on comments except for your own posts), could it be considered an earlier example of demetrication?

I'd agree HN is an example of demetrification. I would add a caveat though: HN's opaque rules about rankings, flagging, when to silently ignore votes, etc would drive me crazy if I didn't trust that the people running it genuinely want a good community for hackers. Give Facebook the same power, and I'd assume such powers would be used for nefarious purposes, and I'd find myself (rightly or wrongly) calling half the posts in my feed part of some sort of conspiracy.