It seems to me that Slack is very vulnerable. Their core product isn't all that innovative and already has credible competitors who could probably beat their price. In fact, I don't understand how they beat HipChat so soundly. I wonder if their next tack will be to start digging a moat of proprietary tooling now that they have a critical mass of adoption.
The updates they put out for Hipchat during slacks rise were new emojis.