Agreed.
More backstory:
I am a member of three slack teams, two for the companies where I work directly, and one which is a loose group of 25 consultants who “chat” about what’s going on. It’s that group who really need Discourse - NOT chat.
I don’t mean to derail the direction of discourse, but yeah, for loosely affiliated groups, a copy of Discourse is going to be far more useful long term than instant messaging tools like slack. Having it in a desktop app means I can command-tab to it when needed, and not just forget its there like any other website.