... on a free plan specifically advertised as supporting unlimited users, and advertised with an open source discount "coming soon".
On a service where all paid plans charge per user, starting to pay when you reach a point when their free plan is no longer suitable for your high number of users is always going to be a ridiculous proposition for even the cheapest plan. The Slack pricing structure is not designed for this use case.
He never said he had no intention, I just think he didn't want to pay half a million dollars for slack.
He wouldn't have paid $50,000 per year either. It's pretty obvious he signed up with the full intention of staying on the free version forever.