I do wonder, though, if this were (re)written today, how much of it would be the same, how much of it would be outdated, and how much new stuff the haters would come up with.
The chapter on file systems is mostly no longer relevant (some file systems do still suck, but the defaults are pretty solid now). NFS still sucks (IMO it sucks more than it used to), but far fewer people need to use it nowadays. C and C++ are still unfortunately prevalent, but there are at least quite a few systems programming alternatives, and they're gaining ground. Sendmail isn't the only game in town anymore, and I expect most outfits use something else these days, and USENET is a distant memory for most people, so there go another two chapters.
But then the terminal/TTY situation has barely changed, and how all that works is just as (if not more) divorced from the reality of daily usage. Security has improved, but most people still have a god-mode root account, and most of the security improvements have come out of necessity; the world of networked computing is much more "dangerous" today than it was in the early 90s. Documentation is still often poor, and many systems still seem designed more for programmers than less-technical users.
I wonder what they'd think of systemd and Wayland!