Agree.
To compare, I started to write an alternative with GenServer as you described. I had also a registry to be able to cast by name during the lifetime of the channel, and the solution based on Task.Supervisor.async_stream_nolink/6 wins in simplicity.
The cost is less throghtput, but as a first implementation of this service I prefer to keep it simple first, and introduce the GenServer if usage shows it is justified. On the other side, the synchronous approach would allow us to send an ACK status back to the client (not a requirement right now, though).
Thanks man! 
