You make me think of a way for every user to make their own members only club, by filtering, and they 100% control who is visible in it; others can view through another's filter:

1. every user can config a "whitelist" of users, to personalize HN to only show comments from those users (and access other users via parent links). This is the "filter", of who they "follow".

2. you can set your whitelist to be the whitelist of any other users. This is "subscribing".

Some few users would end up working to maintain detailed whitelists (like, who they "follow"), and most others would just "subscribe" to them. New users would be left out in the cold til one of these services picked them up (like new bands getting signed to music labels?)

No way would pg go for this, but it's interesting to me. It's sort of a variation of subreddits; and a bit like the various newswire services (like reuters etc) being picked up by local newspapers...

Actually, none of the two items were on my mind: you are a member but you don't own the club to set the rules. You are just allowed to invite someone else in. I'm not sure manually whitelisting scales.

Yeah, it's a different idea, but inspired by yours. Good point about scaling: perhaps your whitelist could include selected whitelists of others; you can aggregate whitelists.