Since they're already likely decoding and parsing the websocket protocol to proxy it, it'd be nice if they offered something like "SockJS-as-a-service", where Heroku handles all the different connection termination types, and just exposes a plain websocket (or maybe a raw TCP socket, even!) to your backend.
The way I've handled it in the past in Varnish is just to look for the upgrade request and do basically: "Whao they wanna do websockets? I give up, return(pipe);" which means Varnish will from then on just ferry bytes from one sock to the other.
