YouTube with a bit more work would make an amazing social network. Like games, people tend to share/centralise their conversations around a type of media - it's why Steam & Discord are now technically popular social networks.

A proper investment in a social sharing feature centred around your friends on YouTube would be a great idea. Not only for watching together with friends but for sharing it privately (just look at how popular video is on Snapchat). They even have a stories feature already - but for YouTubers to talk to fans!