Greetings from the Discourse team 
First of all, thank you all very much for your insights! I’m going to be writing a blog post to clarify our stance on the whole “Discourse (forum) and Slack (chat)” conundrum. As you’ve already concluded, the short answer is: Forum & chat can and should co-exist perfectly well. It’s just a matter of recognising their individual strengths and weaknesses.
I only have one more thing to add to this largely complete discussion: I find it odd that no one brought up the fact that Discourse is an open source Ember application. discuss.emberjs.com is hosted for free on Discourse.org’s servers. If anyone ever wants to make a plugin to improve any part of your workflow, such as:
- improving our Slack integration
- making Discourse more “real-time” (for instance we recently added “Who’s writing” capability)
- integrating your Discourse with canonical resources in the Ember ecosystem, e.g. https://www.emberaddons.com/
then you can do that.
I’d also recommend replacing Disqus with Discourse on Ember.js Blog. There’s a lot to be said about Disqus but I’ll just boil it waaay down to: Open source (and Ember-app) is better.