To me this is where the entire model breaks down and becomes 100% centralized.
At the very least, I would expect that there would be a configurable list of such trusted directories, entirely decoupled from the protocol itself, similarly to DNS roots or CAs.
And few enough people will do that so Bluesky can just kill off support for it when the service becomes popular and they move to the extraction phase without much opposition.
Remember all the chat services that supported XMPP before they killed that? Same level of guarantee here. If most users are expected to choose the centralized option it might as well be the only one.
To me this is where the entire model breaks down and becomes 100% centralized.
At the very least, I would expect that there would be a configurable list of such trusted directories, entirely decoupled from the protocol itself, similarly to DNS roots or CAs.