Interesting to see, but I get the impression (purely anecdotal) that once companies have picked Slack, they'll stick with it for years to come. It quickly becomes part of their core communications, and moving to a competitor or back to what they had before is not easy to do (for purely organizational or people reasons, nothing technological - I've only ever used Slack as a very fleeting communications medium, I've never seen it used to drive automation. Maybe some reporting like 'build xyz failed' or 'there is a new issue', but that can be easily switched back to email).
