I think it's a bit of a chicken and egg problem, which centralized social media solves with advertising.

Msybe I'm asking the wrong questions.

What incentive is there, to run a premium relay, among free relays? Would someone pay for the identical Facebook experience, when someone else is getting it for free? Premium might imply "faster" or "more available" but Clients by design connect to 10 or 20 or more relays, so it shouldn't even matter if half of them are "faster".

And you're right, "locked-out" is meaningless, unless the premium relay has content, which cannot be shared to another relay (not sure how that would work, unless the majority agrees not to re-post premium content).