You could maybe also consider the Mastodon Server Covenant as being a "bloc" of servers
e.g., they could publish a federation "accept list" of all the servers that have agreed to it, and have a process for appeals or challenges, and then you could subscribe to that and only accept instances that agree with the covenant's terms.
For me, "coalition" felt a little weird because it implies to me a political power, where as I'd say "bloc" invokes trading power which is perhaps closer to what we're doing: trading Activity's between different ActivityPub servers. "union" could work too.
#moderation #fediverse #TrustAndSafety