I know what you mean. The Basecamp approach applies even if you don't have a physical office - we work remotely most of the time, but have similar "library rules" in place for Slack. Took some time to get people to follow them but it's not impossible.
I wish we could quit Slack altogether. It makes it too easy to people to disrupt each other's work. Unless the office is on fire, send me a well-formulated request instead of doing it one line at a time and flooding my screen with popups.
