Twitter can't afford Slack. Twitter's market cap is ~12B. There is no way in hell that Slack would sell for less than 10B. They probably wouldn't even sell for that much.
Is Slack, unprofitable w/ $30MM yearly revenue[1], really worth almost as much as Twitter, unprofitable w/ almost $2BN yearly revenue? That's a lot of growth to account for.
Probably. Allowing people to create chat rooms/channels is another possibility, and allows them to enter the enterprise collaboration space. Competes easily with HipChat and Slack. Most people already have twitter accounts, so groups of people can collaborate on the fly.
