Unix's (technical) history is mostly old now
Yesterday I wrote about how Unix swap configuration used to be simple and brute force, covering a number of cases from V7 Unix through Linux 0.92c. As I wrote that entry, it became increasingly striking to me that the most recent time I mentioned was 1992. This isn't something unique to swap handling, or new in my entries about much of the (technical) origins and evolution of Unix. Instead, it's because a lot of Unix's technical history is at least thirty years old now.
It's not quite the case that nothing has happened in Unix history since the early 1990s. Very obviously, quite a lot of important social things happened around 'Unix', such that by the end of the 1990s what Unixes people used had changed significantly (and then in the 00s the change became drastic). Less obviously, a bunch of internal kernel technology changed over that time, so that today every remaining common Unix has good SMP and in a far better place for performance.
To some degree, technical evolution has also continued in filesystems. The problem is that this evolution is very unevenly distributed, with the most advanced filesystems the least widely used. Unix has made valuable strides in commonly used filesystems, but they aren't drastic ones. And the filesystem related features visible to people using Unix haven't really changed since the early 1990s, especially in common use (there has been no large move to adopt ACLs or file attributes, for example, although file capabilities have snuck into common use on Linux systems).
Some things that were known in the early 1990s but not very adopted have become pervasive, like having a /proc or interacting with your kernel for status information and tuning through a structured API instead of ad-hoc reading (and sometimes writing) kernel memory. However, these changes at least don't feel as big as previous evolutions. It's better that ps operates by reading /proc, but it's still ps.
I think that if you took a Unix user from the early 1990s and dropped them into a 2022 Unix system via SSH, they wouldn't find much that was majorly different in the experience. Admittedly, a system administrator would have a different experience; practices and tools have shifted drastically (for the better).
(It's possible that my perspective leaves me blinded to important things in Unix's technical history and evolution in 2010s, 2000s, and 1990s.)