I think people often forget federation is not a new thing, it’s a first design for internet communication services. Email, which is predating the Internet, is also federated network and most popular widely adopted of them all modes of Internet communication. It also had spam issues and there where many solutions for that case.

The one I liked the most was hashcash, since it requires not trust. It’s the first proof-of-work system and it was an inspiration to blockchains.