I suspect that they are killing it off because underused but also because they want to make the chat functions more general. As I briefly had access to a new button on the regular youtube pages that was a speech-bubble. When I clicked it I got a list of recent messages including a message from youtube telling about the new chat feature. It behaves exactly like Facebook's chat in how it creates a smaller window at the bottom-right corner of the page with the chat in it. Which can be collapsed. A few hours later that feature was gone again. I have a screenshot but I need to dig it back u later if anyone wants to see it.