Yes, but what was in it for Vitallium? Continue working thanklessly on a project to serve others’ needs, who has a whole will leave en masse as soon as headless chrome gets to parity with proxy support?

That's not really true. You can use proxies with Headless Chrome using the --proxy-server command line parameter. And the API is richer that PhantomJS. See the underlying API documentation here: https://chromedevtools.github.io/debugger-protocol-viewer/to....

It's only for proxy without auth. So mainly local ones. There is no way to use username and a password right now for proxy with headless chrome.