Every app/platform in today’s world should have every feature possible so since you already have contacts/friends/connections in Facebook/Twitter/Google+/etc, you might as well have them in YouTube as well. And since you have contacts, you need to have chat, otherwise, what’s the point? So in case there was some debate about whether YouTube was a social media network or not, there shouldn’t be any further discussion :)
See the intro video (and chat about it with one or more friends) here

Also published on Medium.