>This is because of the widespread assumption that anything that goes over port 80 is HTTP 1.1, which makes some middle-boxes interfere with or destroy traffic when any other protocols are used on that port.

I'm not convinced that's a real problem once traffic leaves your servers/CDN. In practice I have seen lots of protocols use port 80, since 80 is the port that's most likely to be unrestricted on even the strictest corporate firewalls.