You could put it as PID 1 (with a small amount of modifications), you could put it as login shell (with a small amount of modifications), you could put it in your shell login script, or you could just do tmux a whenever you log in and tmux is already running. You can also save tmux sessions via a plugin. You can also configure each tmux window to open a specific program.
With tmux as an OS, you end up with a TUI web browser (there are several). While you can watch pictures and videos in a terminal, and vim keybinds are strong in a TUI web browser (reducing a learning curve), I wouldn't want the option to run a GUI web browser to be unavailable. So it makes more sense to have a tiling WM/DE, where with one keybind you to your terminal being fullscreen to your terminal multiplexer. But sometimes you want it floating! Then you put it (back) to floating. I also think that you can set up sway pretty much like tmux, except for the resuming/session part. Although my sway config (back when I ran sway) had an auto start of different windows with different applications.
Rooms 1986 project reminds me of Project Looking Glass [1] (or rather: the other way around). Rooms probably also inspired SGI IRIX' fsv (as seen in the movie Hackers from 1995), and Doom as a file manager. Still, I think the 3D exploration of your computer is neat. I don't know if VR glasses allow for this (they probably do), and I also don't know whether the sacrifice (it costs money, and you lose vision of your surroundings) is worth it. As such, I'm usually reminded AR is the better option, except if you want to be fully immersed. Which you very well might want to be while working.
Now, is all of this necessary? Opinion. I believe the macOS HIG is already so good (with other HIGs getting closer) that the answer is no. And for a quick terminal, you can just have a quake-like keybind (Ctrl + ~). On macOS, too, there's multiple ways to add tiling.
(There's also zellij, tmux clone written in Rust with sane defaults.)