Earlier quoted context omitted.
We do not need federated messaging at the consumer app level, we need a replacement that's available at the cellular network level (just like SMS). RCS ( https://en.wikipedia.org/wiki/Rich_Communication_Services ) is trying to do this, but it might be too little too late.
In practice RCS is entirely run by Google outside China, the path to federation was killed around 2019 when Google decided every MNO should eventually move to Jibe if they wanted access to a global interconnected RCS, same on the client side. I don't think it's too late as iOS finally supports RCS. But so far Google hasn't shown willingness to let unsanctioned clients connect to Jibe.
In practice, RCS is run by carriers in most of the world. They connect to hubs, the same way SMS hubs work and also have Universal Profiles.
Jibe is not small, but it hardly runs the worlds RCS. Maybe you're conflating the US with the world?