Comment by Spivak

I mean we're heading there with /usr being your /System. Redhat/Pottering are doing heroic work in this space.

    /Users -> /home
    /System -> /usr
    /Data -> /var
    /Config -> /etc
    /Boot -> /boot
    /Ephemeral Temp -> /run
    /Persistent Temp -> /tmp

The only real holdouts are proc/sys/dev which are the kernel and mnt/media/opt/srv which are really for the user/sysadmin and aren't really used by the OS anymore.