People compare these federated social platforms to email, as there are many email providers and they can all exchange mail with each other. But there's no concept of being "defederated" in email. Or is there? I just don't understand the term.
The entire instance is sort of "shadow banned". Everyone on it can post, but no one will ever read it (except for the few dozen people on that instance). Since forums have some minimum number of users/readers that if the number falls below this people just give up and go away, it will be dead within a month.
Not only is it like being shadow-banned, but you get to be shadow-banned for what the other people on the instance are posting.
The Fediverse might be a good model for a Twitter-alike (it's debatable), but I don't think it's a good model at all for a reddit-alike.
Conversations aren't meant to always be civil. If you enforce that harshly, it turns into a place to post cat pictures.
- Over time, a few instances will grow to dominate and nobody will defederate them because they are too big and you'd lose too much/make too many people mad. These will be the Gmail, iCloud, Hotmail, etc. instances.
- As they become larger, instances will be motivated to follow established politics of the big instances so they don't get cut off.
- Small instances will exist as echo chambers for certain unpopular points of view and mostly none of the big instances will federate them. Porn, Nazis, KKK, Anarchists, religious extremists, etc.
- Possible large bifurcations may develop, e.g. "Fox News/Breitbart" vs. "CNN/Huffington"; each has large followings but they would probably not federate each other.
- New users who just want a place to do normal Reddit-like stuff will be confused by all of this.
Speaking as an admin, if a server starts sending me hundreds of spams an hour, it's going to get blocked because I don't want to spend (my limited) resources on spams, much less push the handling of that down to my users.