I don't think I will move any substantial business communication to Google Chat. I'm happy there is competition but Slack nailed it and now google is playing catchup.
I don't think Slack really nailed it any better than Google hangouts, other than it's IRC like interface that differentiates it. It's chock full of it's own horrible bugs and problems. I can't even have it open for more than a few hours before it slows my system to a complete halt.