Comment by Moxie Marlinspike

One of the controversial things we did with Signal early on was to build it as an unfederated service. Nothing about any of the protocols we’ve developed requires centralization; it’s entirely possible to build a federated Signal Protocol‑based messenger, but I no longer believe that it is possible to build a competitive federated messenger at all. In some circles, this has not been a popular opinion. When someone recently asked me about federating an unrelated communication platform into the Signal network, I told them that I thought we’d be unlikely to ever federate with clients and servers we don’t control. [...] It creates a climate of uncertainty, never knowing whether things will work or not. In the consumer space, fractured client support is often worse than no client support at all, because consistency is incredibly important for creating a compelling user experience.