Here is the relevant issue: HTTP/2 support · Issue #258 · elixir-plug/plug · GitHub
TL;DR - there are some developers exploring HTTP2 with Plug and Phoenix already (potatosalad is awesome). There are also production ready implementations of HTTP2 in Erlang (Chatterbox) beyond the one in Cowboy master. If you need HTTP2 and you cannot wait for Plug/Phoenix, then you can always use directly from Cowboy master or Chatterbox.
