> Slack, Google, and Apple all see the possibility of people overdosing on their services. Each offers its own “do not disturb” mode—Slack unveiled its version just last month—a message to fellow chatters that says you’re busy. The features let people read and respond to messages at their leisure, instead of in real time—which sounds a lot like e-mail.
So you can use group chat just like email when you need to, and as group chat when you need to. It's a very common practice (in my experience) to send a few rapid fire emails, and then switch to chat to discuss.
In future Group chat may evolve to be Slow-First, instead of Fast-First: Present an email style interface - no chat context, lots of white space, Subject line, etc. Then if you are both online and the recipient(s) respond quickly, dump the email stream into a chat window.
Or the other way around. When a conversation slows down to less than 1 reply per 5 minutes, it will quietly minimize itself and later archive itself.