Founder of Envolve here; yes, we did build a version of Envolve for HN called envo.lv

It was always intended to be a marketing gimmick. The critical mass required to sustain good conversation only lasted for the time the story was on the front page.

Getting a website owner to install a chat system, (rather than just having an overlay) combined with integrating with site credentials will make an on-site chat system significantly more viable.