I don't think the audience of people that are willing to leave *just* so AI can read their stuff is big enough to really think much about, at least right now. But the anti-scraping and AI paranoia will obviously push platforms that are willing to play along into functionally private websites.

So I expect the actual bifurcation in practice at the platform level to be "kind of site that cares more about being an open platform than getting boycotted by antiscrapers" and "kind of site that doesn't mind being sort of private if it keeps users happy and the deluge of AI scrapers away".