This is exactly what people on reddit used to say about reddit six or seven years ago. I have to believe the decline in general quality, and the quality of the front page most of all, in reddit could happen in some form to HN, without vigilance on the part of users and mods.
There seems to be a remarkable difference between what people feel HN should be, and what it actually is. "Quality" seems to be more of a sliding scale which correlates to personal bias, and perhaps, a feeling of alienation brought about by a diverse community, than anything objective.
The community will drive to a common form which is shaped by the community managers (mods and power users). I believe @pg gets that and the people taking over also get. Additionally some users may simple outgrow the community even if the community stays exactly the same.
I think HN gets a lot of things right to foster what I enjoy, which is intelligent conversations about a wide variety of forward looking topics. I think the biggest risk at the moment is spamming the site with what are essentially targeted ads/click bait because of the user base is, but for the most part the front page is decently curated.
Interestingly, as long as the discussions continue to contain valuable — and often educated — insights, I personally think there's still enough value to keep coming back to HN there alone. The subjective quality of links themselves may shift as the community ages, but it's the well-thought-out discussions and insights within them which are arguably often more worthwhile than the linked content itself.
It's worth mentioning that comments which don't seem to add much to the conversation are often down voted lately, which is promising.
