As others have conceded below - it is still useful for tight-knit communities who can run private relays for trusted members, but trust percolates all the way up.
The massive relays will eventually need payment or identify you as valuable (or both) to serve you, which leads to familiar methods of monetization. Of course you can take your key elsewhere, but you can on traditional web as well (just include a signed message in your profile).
And once these massive relays get their network effect and economies of scale, the accountability for global communication then again rests on the hands of a select few - but at least "bUiLd YoUr OwN TwItTeR" becomes much, much easier and doesn't require people to migrate clients or authentication - but it always tends towards economies of scale and relays generally centralizing and monetizing.
I don't bring this up because I am a doomer on freedom tech, but because I enthusiastically believe the problems are solvable and that valuable work is left to be done.