Really? WebRTC DataChannels seem like they could fulfill your needs. What is it that prevents using something like WebRTC Data Channels and forces you to use TCP based connections?
So when I looked into it last month - its true DataChannels would be the answer. But I couldn't find any "nice" abstraction in the language i'm using for it. like I just can't get some standalone WebRTCDataChannels abstraction - many WebRTC libraries don't have implementation for this or its all very specialized for audio transfer. There is a route of using some standalone WebRTC gateway service that your application can send messages to (I think this is the purpose of Janus?) - blah blah point is: its not easily done. Not in Elixir so far anyways.
And the second part of it is - I'm sure its easily done but at this point there is some incentive to keep whatever implementation you have to yourself.
Or maybe I missed something and I should try looking into it again.