Comment by yesbabyyes

They have rolled out something along these lines by integrating the chat in Google Meet with Google Chat (or whatever the Gmail looking interface is called).

It was a huge surprise when the whole company suddenly got notifications about chat messages in various meetings they were invited to (but wasn't participating in) as well as messages sent after the meeting was closed.

That said, I think they are on to something here and I wouldn't be surprised if they manage to make some inroads. It will take a long time though given how much of an organization's operations are running on Slack.