TBH this would be awesome, and more people would use it than that dubtrack thing. This is basically like that plug.dj cubecraft used to have and it worked basically the same as this, users could join and play any music they want as long as it was from youtube and soundcloud, this has Spotify support which is even better. In the first weeks or so of this being added loads of people will use it but after a bit it will die down to the point where only like 10 to 20 people on at one time, which can easily be managed.
Plus the addition of making people DJ's can help manage it.