I guess it's a cool idea. No shade meant at all, as obviously you've done more than me, but this seems to be missing quite a bit.

    ls /bin
    bash  fb  ip  localfs  login  mingetty  netfs  pipe  resmgr  sh  sysvinit  tty

I assumed "ip" was the tool from the iproute2 package, but typed in "ip a" out of curiosity to see if this really set up some kind of virtual devices, and it has hung ever since, not dropping me back to the shell. crtl-c doesn't seem to do anything. There is no /etc/passwd or /etc/groups files, so whoami and groups can't map the ids to names. The login is weird if everyone is root. Why not just drop straight to the shell? It seems to exist only to be able to set the environment variable for a user name, but it's not actually a username.

It seems you can run shell builtins that don't depend too heavily on having real proc, dev, and sys filesystems or FHS compliance, and that's about it? Is there a way to write a file? Attempting a heredoc gave a "resource busy" error. Redirecting echo to a filename didn't complain, but there is no file present after doing it. echo $? says bad file descriptor. Is there a way to query exit status of the commands you run?