With respect - you are reading something that wasn't necessarily there, the person you were responding to said nothing about expecting Slack to change their business model.

Which sounds like another reason Slack is inappropriate for open source communication. Money is a completely valid reason.

That still doesn't make Slack an appropriate choice for open source. Even if the project didn't mind paying, Slack's business model is wholly incompatible with the traffic that an open source project would expect (lots and lots of not very active users)