Noodle says wow its been forever. Cool rolling explosions and good call on the animations. Idk about this background music player thingy. sounds unnecesary.
Sounds perfectly necessary to me. Remember GE's Multiplayer clearly enough? Certain songs were randomly picked from a set, depending on the map. From what I see, this would replicate such behavior, and allow all of the epic remixes of music for GES to be in at the same time.

For example, Cradle could have both post and pre-beta3 Cradle Music. (I like the pre-beta3 music personally, but both are awesome.)