False dichotomy. We can and do already have both, on multiple forums, and even on the big social media platforms. That's the case despite there being a few large entities, just as small restaurants continue to exist despite the existence of MacDonald's. The premise that "centralization" of the internet through FAANG gatekeepers forces people to adopt either one or another model as universal to either accept or reject those gatekeepers is fallacious. Centralization of attention isn't centralization of the network.
If this trend of fact-checking causes too much bad press and hassle for social media platforms, then platforms will simply stop fact checking or people will turn to alternatives. But the internet isn't going to turn into an Orwellian thoughtcrime dystopia nor will it turn entirely into 4chan.
An example of what, the existence of other forums? Hacker News.
An example of different styles of moderation on the same platform? Reddit. Some subreddits are very loosely moderated, some are strictly moderated. See: /r/politics vs. /r/askhistorians.
An example of people moving to alternative platforms? Plenty of Youtubers are advertising their content on their own domains or services like Nebula because Youtube's own algorithms make monetization unreliable. Whang and Corridor Digital are two examples I can come up with off the top of my head.
An example of multiple points of view being expressed on large forums, despite the existence of fact checking? That should be obvious - discussion about these topics was never actually stopped or even hindered by the presence of fact checks. You can still find plenty of anti-vaxx content on every platform.
If this trend of fact-checking causes too much bad press and hassle for social media platforms, then platforms will simply stop fact checking or people will turn to alternatives. But the internet isn't going to turn into an Orwellian thoughtcrime dystopia nor will it turn entirely into 4chan.