Why are people speaking of Slack in the past tense? I'm as much of a software liberty zealot as it gets and will never understand people flocking to "platforms" when we had open protocols for chat for decades (irc, xmpp), but Salesforce certainly is a respected company having pioneered SaaS long before that became a thing in this decade, isn't it? At least I remember Salesforce being looked up to by the likes of SAP and Oracle 12-15 years ago.
My view on the acquisition is that Salesforce needed a "chat" communication tool so instead of building one they purchased one. This is smart. However, it will require Slack to change to fit into the product catalogue, and that change is what will kill Slack.
This is unlike the Heroku acquisition in 2011, where Salesforce just wanted to enter into the "cloud" market but didn't really need to bundle the product into the rest of their systems. As far as I can tell, Heroku came out fairly unscathed and used the money to improve themselves/continue operations.
I think the Slack as we knew it is probably not long for this world. It will be absorbed and mutated to live inside Salesforce.
Ah, I can now see the fear that Slack will be taken away from people who're used to it. Personally, I've had only a brief encounter with it, and that was clearly driven by a project lead in a SV bubble, as in, everybody's doing it, so must we. But I'd imagine that Salesforce management isn't so stupid as to spend that kind of money only to loose customers. I know that Salesforce has made inroads into eg time tracking and invoicing for freelancers at large consulting companies, so there's definitely a market to grow into that's not entirely alien to Salesforce's core business, even if they don't start from a tech but business administration angle. And Heroku still doing what they did ten years ago, if anything, is rather a sign that Salesforce will leave Slack as it is, isn't it?