If community mods on different servers saw they have similar moderation guidelines, they could agree to federate. If they diverge in the future or disagree, they could defederate. Just like instances can defederate from previously federated servers today. It would be no more or less disruptive than defederation is today.
Heck, if done thoughtfully, it could even allow cross moderation, multiplying the number of mods for like-minded communities. The only mods who wouldn’t appreciate that are the egotistical, power hungry, Redditish mods.