I would agree with and extend your remarks with bot percentage only increases over time, there's a repellant mechanism that pushes away humans and no mechanism at all to lure them back once they've been pushed out of a site.

Eventually you end up with stackexchange or Reddit or 4chan where 95%+ of posts are bots or at least LLM generated, and the remaining 5% is crazy people who refuse to leave. HN is behind in that cycle but will inevitably and unavoidably catch up because as I stated there's no repair mechanism. All successful online orgs and communities attract bots and LLMs that kill the organization. There is no immune system other than unplugging and touching grass IRL.

My guess about "large scale socioeconomic effects" is we can't talk about Dead Internet Theory in public in polite company, but we can talk about "too much LLMs" or whatever in a vague sense while describing all the symptoms of Dead Internet Theory. Like those people who complain about poop on the sidewalks but can't be permitted socially to declare any sort of dislike of homeless people, so the talk is focused solely on the symptoms as if the symptoms appeared magically, an uncaused causation. The advertising fraud bubble will pop, eventually, and it'll all be blamed on LLM bots on social media, it totally wasn't planned and aided and abetted by the companies themselves, no, LOL. Their profits off advertising fraud were totally accidental and unintentional, you see, so they should get away with it. The people to blame are those vague AI bot things that magically appeared and totally had no legally prosecutable humans behind them.

Another large scale effect to talk about is massively pulled forward demand. A decade or two of Facebook and that pulls a lifetime of demand forward. What happens when the bill's due and nobody left but a tiny fraction of hopeless addicts? If the population as a whole does a lifetime of doomscrolling in 20 years, the next generation at least will be a total drought. Internet access will never go away because its too useful to pay your bills online, but social media will almost certainly go the way of the late 1970s CB Radio crash. I assure you CB radios are still being made, people still making money off them, and people are still using them, however only a microscopic fraction of the population uses CB Radios. So it will be soon, for "socializing online".