This is worse than retrocomputing; it's necrocomputing, a pathetic attempt to mate with the corpse of a dead concept operating system. Instead of drawing any interesting lessons from Plan 9 for OS and distributed system design, it's an attempt to turn a burned-out wreck into a daily driver, generally by redefining driving as "sitting in a car and making brrr noises".
They are remarkably honest about it: "There is no advanced auto-completion of program names and flags, like hipster zsh and fish users might be accustomed to. But this really isn't an issue since Plan 9 has virtually no programs or flags to speak of, as you will discover soon enough."
Those with any kind of spidey sense for going down tech rabbit holes might also notice how front-and-center features for, ummn, connecting/emulating computers not running Plan 9 are in this guide.
Randomly cutting into the document presents you with a plethora of the usual fetishization of the fact that a nearly useless operating system, window manager, etc. doesn't take nearly as many LoC as something that more than a handful of people use, not to mention a giant list of things that you apparently shouldn't do, like use files made in Office: "There are a great many office suits (sic) on most operating systems, and other office utilities besides too numerous to count. So many are the choices in fact that it's easy to forget that "office" is just a fancy word for working with text."
It seems to close on some daft explication of how everything can be a database and how you don't need a real one, presumably after having invested thousands of words on how you don't need a spreadsheet, don't need a web browser, don't need an office suite, etc.
I cannot think of anything that captures the spirit of Plan 9 less than attempting to revive a dead, nearly 30 year old operating system and pretend that it's a useful daily driver. At the time Plan 9 was built it was a quirky and clean take on technology of the time, built on cutting edge and interesting hardware. At a time when distributed systems in Unix (not really Linux, then) were a tooth-grinding exercise in frozen NFS mounts and awkward, irritating incompatibilities, Plan 9 was a breath of fresh air. Honoring its spirit would be building a new operating system that applies this kind of simplicity to modern hardware (a hell of a task) - and learns from its mistakes, not trying to set up a homestead in this utter wreck.