Source: Reddit
Another important bit is about new Music app on Windows Phone 8.1, which is actually Xbox Music app built in the OS now. According to Joe Belfiore, the new Music app will be able to get updated via Windows Phone store, making improvements more frequent.
@wiiggin yep. The Music (aka Xbox music) app built into 8.1 is much improved. And store-updateable.
— joebelfiore (@joebelfiore) April 7, 2014