Maybe the solution isn't federation, but a nonprofit foundation with an open source and relatively simpler codebase like Wikipedia. Wikipedia is the 800# gorilla in that space, but there's no ads and no perverse incentives and they aren't trying to lock down to prevent "theft" from AI companies, and the decentralization is through people being able to relatively easily setup specialized wikis.

I'm not sure the problems of federation are ever going to be solved at massive scale. Usenet and IRC were always problematic back in the 90s. Not even e-mail works well due to spam.