The only difference between email and federated IM is email started out (mostly) federated and IM systems started out (mostly) not.

Only inertia is what drives this skepticism of federation in IM.

Just as there is no technical reason GateKeeper couldn't succeed on iOS just as it does on macOS, there is no technical reason federation couldn't succeed in IM as it does with email.

Just perceptions have to change.

> Ultimately most users just don't care about federation. Them's the facts.

Not really. Everyone is annoyed by this issue. But there isn't much they can do. People need to register on N different services and use N different clients to communicate with users of those networks when they need to. Do you think they appreciate this mess or find it highly convenient? But they don't have any other option (except may be not communicating with some of them at all).