At the time, Google said other game developers would have to wait a while:
We will continue to add new partners and new features in small steps, starting with today’s release of the games APIs to a small number of developers. We’re keeping a close eye on feedback, and are eager to open up more access as soon as it’s ready.
Now, a source has pegged November as the date. Look for the explosion of games on Google+ to come after that.
Google is taking its time opening Google+ to developers — it just released the first Google+ API last week.