I think some of the Mastodon problems about usernames and so could be solved by a federated trusted login/user server apart from the messaging server itself. So, a user could create his login on a server and use it on other servers, somewhat like a Kerberos/AD system
@HufflepuffBR basically i think federated logins would just be abstracting the login problem into an even smaller federation where more problems occur if a single instance goes down