Picture in picture is a cool idea, and I think it was executed really well, my only issue is that it doesn't currently support the Twitch player either in live form or in VOD form (as far as I can tell).
I don't know if it would be possible but I think it would be awesome to allow the PIP function to work with the Twitch.tv video player and allow folks like me to watch VODs or livestreams while doing other things. 🙂 ❤️