Federation seems to have its issues though, unfortunately. I created a post on lemmy.world earlier today (in hardware@lemmy.ml), and it took about 15 minutes for it to show up on lemmy.ml and sopuli.xyz.
If we consider something that is breaking news, 15 minutes is WAY too slow; there will be tons of duplicates posted from dozens of instances, even if they are posting to the exact same community.
What would happen to the communities on that instance, though? If they choose to block/defederate then the other instances would no longer be able to access them (or "have all the data"), right?