TFA says "Therefore, we argue that the POSIX era is over, and future designs need to transcend POSIX." So they're actually not answering their own question, they're saying "the answer should be x" which is subtly different. There are a lot of should-be's in computing.
Ironically, while I am an heavy email user, at work it is mostly used for internal newsletters, all the communication happens over Slack.
slack replaced your internal, HR monitored, internal IM. Not email. Just so happens that lots of places were using email as their IM solution.
In case you missed part of my comment I mention the small detail of being an avid email user, but of course you needed to do some tiktok marketing.