This is, fundamentally, the Open Core business plan, which Mattermost is executing quite successfully. You get all the marketing benefits of being "open source", but few IT departments will use your software in production without buying the enterprise license, so you get most of the revenue you'd have had if you were closed source.

Folks have different perspectives on Open Core. It's definitely a lot better from a freedom perspective than proprietary software, so I don't want to be too down on it. But it isn't really FOSS, and I think the difference is important, which is why Zulip is following the commercially more difficult path of 100% FOSS. Even obviously enterprise features developed entirely by our paid team, like SAML authentication are FOSS, and our plan is for it to remain that way forever.

It's commercially more difficult because it means right now we have users at governments and Fortune 500 companies and whatnot who've reached out to tell us they how much they love Zulip, but nonetheless aren't paying us anything. On the flipside, Zulip has been very successful in building a large community of volunteer major contributors (some handy stats are in our release blog posts, e.g. last week's https://blog.zulip.org/2019/12/13/zulip-2-1-released/). I don't think that would have happened had we taken Mattermost's aggressively Open Core approach..

(I lead the Zulip project and company)