Imho one thing that the Signal project suffers from -- and that a lot of open-source projects suffer from -- is poor documentation. They need document their protocol better, to make it easier for third parties to integrate with their system.

Signal still lacks a working desktop client (no, the one that you can use if you're running Chrome doesn't count), and I'm sure tons of people would be eager to do stuff like provide integration for Pidgin if only there was better documentation.