I closely studied plan 9 many times, I unfortunately can't use it because of accessibility issues but from what I read and heard it feels more like a time capsule from the 90s, which is ironic considering it was meant to be a future path for os research. And even in the 90s there were developments in unix that the labs seemingly completely ignored, like DJB's daemon supervision.
To talk about the article itself, the only reason plan 9 can achieve such a design is because it's developed and used by the same small group of people. If linux is a bazaar and BSDs are cathedrals, then 9front is a monastery's citadel. Another thing that isn't mentioned is that both linux and BSD (and pretty much anything based on posix) has a lot of third party software that would be hard to maintain along with the rest of the system, if the monks even include it to begin with. And that software could include something like jq which a lot of software depends on and would love to just assume it's there.
And really, what more does someone get from something like this over, say, having a more or less formal standard on what a true plan9 system includes and waving it in someone's face when they choose to ignore it? This is pretty much what modern unices do and it works out great in cases when it's actually important. Most people don't care what commit your system is built from as long as it works as their programs expect it to.