Every single piece of hardware these days would work a whole lot better when it comes with an upgraded software from time to time. The same too, applies to Google Glass, which has yet to hit the mainstream market big time, although it has been made available to developers for quite some time already. The most recent Google Glass XE11 update was not meant to solely help one out with one’s schedule as well as commute, since it has been discovered that the developers from Google have thrown in support for Google Play Music as well as part of the upgrade.
I would suppose that this particular move would have something to do with paving the way for a future feature announcement. You will first need to sideload the app onto Google Glass, where a new “listen to” voice command will then appear on the the hardware’s home screen. When you decide to utter that particular phrase and speak the name of an album, artist, playlist or song, you ought to then be able to listen to tunes that you have already uploaded to Google Play Music, or to those that are readily available via All Access assuming you already own a subscription.