Not quite a quine or fixed point, but something akin to it in the context of neural nets? A version of the AI "singularity" that is completely useless. :)

That's something many humans already suffer from, due to social media platforms creating large echo chambers.

I think there's enough human-generated content that LLMs won't suffer from that. If they did, you could always manually filter what they train from... only data from websites with trustworthy timestamps pre-2020, for instance, or content after that which might be partially AI generated but still has strong human filtering, like wikipedia and arxiv and scientific papers in general.

SEO is not ads and a pay model won’t stop them.

Maybe. But the cynic in me says it'll wind up being like cable TV or a subscription to the NYT: Since you are well-off enough to afford a $20/month plan, Microsoft will reason, you're the perfect consumer to advertise to. So you get both ads (or at least heavy tracking) and you get to pay.