I think it'll end up like Facebook (the social media platform, not the company). Eventually you'll hit model collapse for new models trained off uncurated internet data once a critical portion of all online posts are made by AI, and it'll become Much more expensive to create quality, up-to-date datasets for new models. Older/less tech literate people will stay on the big, AI-dominated platforms getting their brains melted by increasingly compelling, individually-tailored AI propaganda and everyone else will move to newer, less enshittified platforms until the cycle repeats.
Maybe we'll see an increase in discord/matrix style chatroom type social media, since it's easier to curate those and be relatively confident everyone in a particular server is human. I also think most current fediverse platforms are also marginally more resistant to AI bots because individual servers can have an application process that verifies your humanity, and then defederate from instances that don't do that.
Basically anything that can segment the Unceasing Firehose of traffic on the big social media platforms into smaller chunks that can be more effectively moderated, ideally by volunteers because a large tech company would probably just automate moderation and then you're back at square 1.
Eh, open-sourcing is just good business, the only reason every big tech company doesn't is that loads of executives are stuck in the past. Of course having random people on the internet do labor for you for free is something Google would want. They get the advantage of tens of thousands of extra eyes on their code pointing out potential security vulnerabilities and they can just put all the really shady shit in proprietary blobs like Google Play Services, they're getting the best of both worlds as far as they're concerned.
Large publicly-traded companies do not do anything for the good of anyone but themselves, they are literally Legally Obligated to make the most profitable decisions for themselves at all times. If they're open-sourcing things it's to make money, not because they were "good guys".