I would also expect the authors are going to have a hard time keeping up with Slack. One of Slack's goals in picking their architecture was to allow for experimentation, iteration, and expansion. Reverse-engineering an API inevitably means being behind. And given the number of engineers Slack has, it could well mean being further and further behind over time.
When you're building on someones platform, you take a risk. When you're actively integrating with a fast moving platform, you add more risk. When you build on a platform which doesn't want you there, you add even more.
When you're having to reverse engineer a platform to build something, you're asking for a special kind of hell.
