Last Updated: August 21st, 2014
Update #1 (8/12/14): It looks like Google deleted the tweet embedded below. Between that and the lack of an update to this support page, someone might have pulled the trigger early. But if those countries don't have access yet, they probably will sometime soon.
Update #2 (8/19/14): After a false start last week, the Play Music expansion now seems to be live. The official Google Play country availability page has been updated to reflect this as well.
Last Updated: August 8th, 2014
Perhaps you recall back in 2012 when Google caught some flack for its 10-device limit on Play Music access with only four deauthorizations per year. It was forced to backpedal and allow users to deauthorize unlimited devices, and all was well with the world. Well, until now. It looks like Google has started enforcing a limit of four deauthorizations per year once again. Support docs and the Play Music settings list the limit.