Am I the only one who sees this as anti-competitive? This is basically collusion - Atlassian agreeing not to compete in chat in return for a payment from Slack. It almost seems like we're intent on making literally every mistake we made with traditional businesses, but with electronic products.
Jokes aside, how is this anti-competitive other than trivially reducing the number of total competitors? If 4th place wants to give up in the race, should all of their work be in vain? AFAIK a product like Slack doesn't require tons of up-front legislation preventing new entrants in the race. Competition in this domain is very much alive, regardless of what a few big kahunas decide to do.