In my opinion, it doesn't matter if it looks like Slack. What matters is that I can deploy it on an existing infrastructure and still have control over the service instead of handing over control to a third-party.
And its nice to be able to choose which apps you want to use on all the different platforms; and choose differently than everyone else. The app that works for me isn't necessarily the app that works for others, but I still want to be able to talk to them using the app I want.
hillarious way to advertise, chum.
http://www.businessinsider.com/slack-growth-after-one-year-2...