Signal does not play nice with other protocols and centralizes everything. Hardly an improvement. Better go for real alternatives that will likely survive way longer like Riot/Matrix.
Or 'plain and simple' XMPP with OMEMO [1] encryption. This is easy to host yourself using Prosody or Ejabberd or another XMPP server, Conversations (or one of its forks) on Android, Monal or Siskin or iOS, something like converse.js in a browser, etc.