What if instances could "subscribe" to the list of defederated instances of each other?

So for example. Let's say that Alice and Bob have their own instances, alice.ml and bob.ml. Bob trusts Alice, so he sets up the following rule in bob.ml: "if alice.ml defederates an instance, then bob.ml defederates it too."

Then Charlie starts charlie.ml. It's a bad instance. Alice manually defederates alice.ml from charlie.ml. Bob won't need to do anything - bob.ml would do it automatically.

I feel like this idea would address the issue of playing whack-a-mole, since admins of multiple servers can split the busywork if they so desire, and only with whomever they desire. And there's no risk of a central control going rogue, since there's no central control on first place.

It could be even further refined with more complex rules on when to automatically defederate other instances. Such as taking into account if the other instance did it manually or automatically, or how many among X instances defederated it.