Last year Google said that they would bring Hangouts to the new Google Games. So I would imagine that this new Hangouts app will be the only way to communicate directly through Google Games. So that should give the app a significant boost in users. Once people use it for in game chat they might start using instead of whatsapp ect.
Last year, Google said that Hangouts will be integrated into the new Google Games. So I would imagine that this new app will be required for all chat using Google Games. I also expect that Google Plus account will be required for everything except SMS.