I knew someone who ran it with inittab about 3 decades ago, and I very much doubt they were the only one. Emacs could be used as a full-blown OS long ago. It just depends on your needs.

Also, the psychotherapist was one of a kind ;)

Personally, I could live with tmux or zellij as PID 1. Because from there I can do everything, except GUI. Might as well use Sway then to achieve virtually the same.