Once the fediverse gains significant traction there will be a huge coordinated media smear campaign to associate it with extremism, CP, violent crime, terrorism etc.. The "won't anyone think of the children" attack will be leveraged to ""regulate"" the fediverse (probably by legacy social media like Meta alongside the security state), aka transform it into regular old centrally controlled social media. Upload filters, encryption back doors, know your customer laws etc.. Non-regulated decentralized social media will be attempted to be made illegal, not sure if it will succeed.

So yeah eventually any true decentralized social media will have to move completely into the "darknet".