Provocative thesis: email is an example of the failure of federation.

The API is frozen because of the gigantic size of the deployment. The API is inadequate. Spam has destroyed email as a result. We cannot fix it, because getting the API right early didn't happen.

(Also: please argue with me and convince me that I'm wrong & this can work. I need Twitter to die a well-deserved death for their failure to take proper care of their one good idea.)
@ceejbot ultimately it all depends on you, amongst others. will you keep posting here so that other people will have it easier to switch or not? :)