I'm not sure about that. Right now (apart from ideology), there are probably two major reasons why someone would pick an OSS solution. 1) Inside Firewall hosti

I'm not sure about that. Right now (apart from ideology), there are probably two major reasons why someone would pick an OSS solution. 1) Inside Firewall hosting – Slack can easily fix this by introducing a product that works inside your firewall, and I bet they're already working on it. Their "teams" model already works perfectly for it. 2) Customizability – Slack already has such a robust API for integrations, that most of your customizability and branding needs can be taken care of through the API and CSS rules. The one thing I personally need for my product is the ability to bundle slack as an embedded chat directly on my site (mostly because I don't want users to have to install a separate app), and I really don't see Slack building that, to be honest.