I've used #email as an example of a #federated service myself. But using email as an example may not say what one thinks it says: how many people still use email for personal communication? They flooded into the commercial silos because email sucks. And email sucks because all the development expertise got sucked up by the commercial silos while ESR completely obliterated free software by convincing people that it was all about how software was developed rather than ideology or freedom.