Elixir inherits those properties from the Beam VM it shares with Erlang - both languages are effectively great for this WS/Channels use case - but Channels seems unhelpful unless you're already using phoenix. I can't see that it can be used in say Erlang.
Channels are really just a protocol, but that protocol is implemented in Elixir (Phoenix) and so isn't available elsewhere.
I think that the important question is "why does this protocol exist?" Most likely, you'll end up solving similar problems as to why Channels exist in the first place. So from a protocol perspective, it's nice that some problems are solved for you.
May not fit your use-case, but you can create an umbrella project with both an Erlang app and an Elixir/Phoenix app, whereby the latter's capable of calling functions in the former.
