Great post, but here are some questions those graphics raise, that I couldn't find an answer to, and which have only my experience with email, usenet and irc for reference (all of which are federated, easy to abuse, had a host of problems, and have slowly migrated to centralized versions to solve these issues):

• how do you ban someone?
• what stops him from spinning 100 amazon ecc instances, federating 100 servers and spamming his thing 100 times from 100 different instances?
• how do you even block an instance?
• what happens with the federated content once the source instance goes down?
• say lemmy.ml and memes goes down, how do you post a new reply in memes@lemmy.ml? does it even work?
• i haven't found any info for syncing accounts across instances (to prevent this loss) or if this is even possible at low level
• what happens with comments and pictures once a federated instance goes down? say, if i selfhost and i crash without backups, does my content and posts disappear?
• can i pull it back?
• what kind of capacity planning would I need to selfhost say, a decade worth of reddit browsing? assuming I only care about my posts and what I save, would they be accessible for me?