Google Play Music support recently arrived for Glass users, and it looks like Google is going to do what they can to ensure this setup gets a thorough testing. Google Play Music All Access subscribers appear to be getting invitations to join the Glass Explorer program. We haven't seen any confirmation direct from Google just yet, however these invites are said to be coming by email.
According to the details being shared, the email brings talk of "VIP invitations for All Access customers to join the Glass Explorer Program." Of course, this means those users will need to be willing and able to shell out the purchase price. Google Glass remains at $1500, plus the applicable sales tax.
But hey, on the bright side, All Access subscribers will be able to join this somewhat exclusive club. There doesn't appear to be a set deadline on the invitation, however the linked page does make mention of this being "available for a limited time." Those All Access subscribers looking to signup will need to be 18 or older and located in the US.
The other requirement is an easy one, you will need to either provide a US shipping address or be prepared to pick your Glass up in person. The in person pickup locations include San Francisco, Los Angeles and New York. Still no word on a full public Glass rollout, but given this Explorer program expansion combined with the previous invite openings -- it seems Google is inching closer to a widespread release.