While not very familiar to many, this is highly similar to the old Lisp Machine environments. Those were similarly a clean break from prior OSes, with:

  - a powerful REPL to call either apps, inline tools, or direct commands
  - interactive shells made up of mouse-interactable graphical components being
      printed to the screen
  - compilation of source code directly into the running image

etc.

They were also single-user, but did networking as well. People logged into a machine remotely could have the same interactive graphical sessions in their own context.

Given the history of computing from the 50s - 80s, this desktop architecture idea comes naturally to a lot of people. The major OSes, however, all have their ancestral lineage which prevents major rethinking. But another issue is that these ideas are at least power-user oriented.

While the mobile market did some major rethinks about the UIs, they're still *nix inspired descendants underneath, and don't expose anything but pre-baked applications to their users.