Pushpin (http://pushpin.org) may be in line with what you're thinking. It separates connection management from backend logic. In fact the project itself is a handful of microservices (Mongrel2 is used as a separate process for the HTTP handling).
Uses GNU AFFERO Version 3 license - noted to save someone else from going from happily excited to disappointment.
Code that can be run, modified, and redistributed at no cost. There are worse deals. ;)
Perhaps a microservces implementation with each step (handshake, broadcasting, http overhead) having their own cluster and communicating through channels.