>An individual should be able to have multiple Discord nyms, right?

Yeah, I think so. I mean this is like my 20th hacker news account. I am using my 5th discord account right now.

But at the same time it would be an interesting to see how anonymous yet sybil-proof social media would work out.

I get the feeling that it's already pretty easy to buy and sell fake IDs, so I don't think it would pan out in practice. I also had the same idea as you: if such a system were to exist, you could sell proofs for all the services you don't use.

Usually, these zero-knowlege proofs are backed by some sort of financial cost, not the bureaucratic cost of acquiring an ID. All of these "linkable" ZK proofs are aimed at money systems or voting systems.

In the blind-signature based money systems, a big problem used to be dealing with change; you had to go back and spend your unblinded signature at the signatory to get a new one. In a similar fashion, maybe you could make it so that users could produce a new ZK proof by invalidating an old one? So you could retire an old nym if you get banned, and create a new nym but you could only have one at a time? IDK if that is a reasonable tradeoff.