Thanks for this suggestion, never seen these guys before but they’re incredibly talented and very enjoyable to watch

It sounds like a cursed item in D&D or something.

The Book of Faces Wondrous Item, very rare

This enchanted tome magically records the likeness each humanoid slain in its vicinity, preserving a snapshot of their life and memories. The book can be read to glean superficial information about it’s subjects. As an action, you can tear a page from the book to summon a ghostly spirit of its subject, which will be magically compelled to answer questions. The spirit knows nothing the owner did not know in life.

The Demon Lord Elgor Ithym is said to have a keen interest in this book…

I would suggest that instances should have settings that allow them to decide whether to “advertise” a community list. With configurable settings like "all, “most active”, “top X”, or even a manually maintained list depending on the admins and instances preferences.

Then your home instance, when searching, should have it’s own settings to decide what results it’s going to ping other servers for. Big/popular/high confidence instances can have an open all/all relationship, while you might query only the top 10 communities from unknown or new instances to handle the scenario you describe.

Federation can be binary yes/no but there should be room to add more logic around enabling search on communities from your instance and controlling the search results from other instances. I don’t think the two are mutually exclusive, unless I fundamentally misunderstand how federation works!