Built in music player
A lot of streamers don't know how to put music in their stream.
In some streams there is music but you (the viewer) sometimes wanna turn it off but you can't since it's a part of the stream audio.
So what if there'll be an option in Twitch to choose music to your stream? That way everyone will be able to use music in their stream and the viewers will be able to mute it if they want and still hear the stream itself, and also see the name of the song if it's not shown in the stream.