Interesting. IBM adopted Slack just fine, back in 2016. I believe they've got at least 100k employees in their Slack workspace. Not sure if it's Slack or IBM doing the hosting/scaling for it, though.
There is a cultural difference between Uber and IBM which would explain why Slack didn’t shown its limits at IBM: Slack people belong to a startup which typically wouldn’t mind get everything done in a chat; whereas IBM is a 100+ years old company where everyone has to fill a paper form and managers type with two fingers (Source of this specific example: I’ve worked with IBM consultants with one of their products). Chat apps do not play the same role in each.
