"No expectation of immediate reply"? HA! I SO wish. Slack kills any async expectation. Specially if you install it on your cellphone. Then you're on the clock 24/7.

I guess the article also assumes different time zones when working remotely?

I filed the article under the "rubbish bin". I've worked remotely for several years, and maybe I live in a different planet, because "async" and remote work do NOT go hand in hand for me. If anything, Slack means people can reach me even when I'm taking a dump, and I'm expected to reply at that moment.