The thing is, as I've seen in this, group chat has a "cuteness" to it. Just like IRC back in the day (or today depending on if you still use it), people are much less formal in group chat and there seems to be less expectation of formality. There is cat pictures and funny emoticons. This isn't a tool challenge; both email and group chat can be equally informal and cute. I contend that email /still/ is a better mechanism given the non-realtime nature of it.
But then again, the realtime nature of group chat is what some like. It's precisely what I don't like. I like 1-1 chat quite a bit, though I very quickly default to video in these cases as well (higher fidelity, quicker, less prone to written miscommunication).
Hipchat/Slack/IRC are great for some use cases that require the type of communication (specifically I think of operations, incidents or things along those lines). I feel other general team communication in these mechanisms is, well, overblown. My gut tells me PRs are better for much of what group chat serves, and if not PRs, email/ML are still great. And don't forget getting everyone into a room or video hangout.
I don't particularly like email, but I don't hate it either. I do, however, very much dislike group chat.