Most companies aren’t fully remote, so dogfooding the common use of Slack seems smart, where it is still a useful tool even if you are slacking someone 5 feet away.
This is very true. I recently moved from a mostly on-site company, where I thought we used Slack a lot, to a globally-distributed, fully-remote one where Slack is the primary form of communication. We use it very differently, as the volume is far higher and we have to deal with timezones. e.g. in my previous job, I found threads annoying and rarely used them as I found they meant messages got lost. In my new one it's a faux pas to not use threads except for in very low-volume channels, because otherwise its tough for people to catch up on channels.
Yeah, that's an interesting point as well. Our product is for gamers, who are usually "remote" (if you can call it that), but Slack may trend towards over-fitting to highly-engaged, fully remote work if they were to do this.