I completely agree with this. I'm part of a group that's trying to help people in the local community learn programming and we're using Slack to chat outside of any scheduled sessions. We're at over 1000 members in Slack now and are seeing messages disappear before the two-week mark. We don't collect any money from our members and Slack's pricing model makes it unfeasible for us. At this point, Slack's search feature is hit or miss when searching for anything over a week old.
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.
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)
