Gnome Music app was being developed in three phases as explained on the GNOME Live wiki. Seif Lofty, the project maintainer, has announced that first phase is almost complete. This phase involves the setup of basic infrastructure, implementation of grilo querying, album view, songs view, artist view, playback support and porting user interface to glade.
Seif Lofty has posted some nice screenshots of development version:
In next phases of development they are planning to implement playlist view, selection functionality on all views, actions, searching and remote resources. If you want to install this GNOME Music application source can be found on GNOME git repositary.