Fediverse

With companies quickly closing their communities to try and keep their user generated content for themselves so they can make money off of AI training data, it's possible the open nature of the Fediverse may cause companies to invest in it. "You let us keep indexing your content and we'll foot the bill for your server" seems like an excellent way to get cheap training data, especially because content gets mirrored between sites.

And truthfully, if there were a Fediverse instance that could handle a million users without collapsing, it'd probably be able to run ads as well.

There's a risk that users will flee the server if they find out about this stuff, especially with services that support moving your account, but I can see someone succeed with a commercially backed Fediverse instance.