This seems to be great !
I think it is similar to OpenVZ concept of controlling VMs from Host, right ?

How it works, if it is not installed in guest ?
Using PV, in connects into guests virtio-tty device ?

In may become more universal, if more command are added, such as: (like OpenVZ does)

vm 101 enter
(this will enter into guest VM TTY, right from host terminal).
-or-
vm 101 exec [guest-command]
(this will execute command on guest, using bash, right from host terminal).

For more commands from OpenVZ, that can be applied to Qemu/KVM, see: (7.8.2008)
http://www.howtoforge.com/installing-and-using-openvz-on-fedora9-p2

-Alexey