However, we are talking about how the scale of HN is getting to the point where people are complaining about S/N ratios and as you say:
>exclude newcomers, aggressively moderate newcomers, or succumb to newcomers.
I think this is shortsighted, elitist or both. First, you/whomever posted this has clearly left out a better option; ADAPT to newcomers/scaling.
While I agree that HN may have been like a subreddit, with a target audience, HN is growing, entrpreneurship is growing, the startup ecosystem in the valley is growing, our knowledge base is growing.
Eschewing newcomers and growth is to operate in fear of progress.
Taking the spill-over and iterating what HN is to accommodate is not to "lose its cred" so to speak...
Further, I am not advocating a straight adoption of reddit, but I do feel that HN can learn a lot from how they enable the community.
I had written a bunch of suggestions in my first reply, but deleted them, but I was suggesting some options along the lines of:
Validate SMEs in given areas and give them high-level moderation/influence.
Post a clear HN-etiquette that delineates posting format/commenting format that the stie wants.
Earn further features/user abilities through karma - such as allow SMEs/high karma users to only create HN-subs.
There are a lot of things we can do, but to cry in the corner over newcomers is never a winning solution.
I'm not suggesting that we do, obviously. However, newcomers have the disadvantage of not knowing the history, the ethics, the goals/ideals. They only know what it was like 'when they joined'. When I joined, I was corrected a few times for missteps I made. The growth rate makes that less and less feasible. It isn't that I hold a grudge to new people, they are just disadvantaged when it comes to the communal etiquette standards.