There are numerous references to "stub domains" in the information about
Xen.  Given the benefits, it would be nice to have the functionality.

Notably qemu and xenstored are stated to be functional in stub domains.
I'm under the impression having xenstored in a stub allows domain 0 to
do a restart/kexec.  Having qemu in a stub adds protection for domain 0.

Initial experimentation indicated the default Xen build setup tries to
download the stubdom source during build.  This could be a challenge.