Wikipedia: "Signal relies on centralized servers that are maintained by Open Whisper Systems." Would it be possible to use the same open source proto and crypto that Signal chose, but in a way that does not rely on third parties to run servers, such as OWS, WhatsApp, Facebook, Google, Microsoft, etc.?
https://signal.org/blog/private-contact-discovery/
Moxie has said repeatedly that they're working to do better on this front, but it's not without its technological challenges. He's written repeatedly about this and has also called for anyone willing to try to make it happen and offered to help them. Just one example springs to mind:
https://news.ycombinator.com/item?id=12883410
And federation is possible over XMPP with Signal: