Very interesting, I'm looking forward to checking out the product! We use GitHub exclusively for everything; even our non-technical team-members leverage GitHub for sales, HR, marketing, blog post writing.. You name it. We did have to build a product to make this easier on ourselves [1], into which we've been resisting integrating chat. Chat is the only non-GitHub piece of our workflow, Gitter looks promising!

[1] http://zenhub.io