I think the games will be sold as a per game bsais on Google Play and other online stores. They specifically mentioned that links to buy games could be included anywhere: Twitter, Facebook etc...
But would the game saves be stored in your existing Google Drive space?
Or would Goolge charge a similar monthly fee as PS+ and MS Live for game saves, online play, screenshots, videos (if not sent to YouTube), maybe throwing in some free games per month..