There isn't a need for fidelity bonds with WabiSabi because no one is paying for anyone else's block space.
What's the connection between block space and fidelity bonds? I understand that fidelity bonds serve a purpose by discouraging attackers from launching sybil attacks, as they would need to lock up bitcoins for an extended period.
I don't know what you mean by "a regular coinjoin".
I'm referring to a system where there's a coordinator and user connection. Users register their coins through it.
The coordinator is not "relied on not to orchestrate a Sybil attack", any non-coordinator entity can be a Sybil attacker
Especially the coordinator, as they are responsible for approving or disapproving coins in every round.
Can you quote your specific message instead? There's a lot of discussion there.