It's at least removing the very obvious user->root
attack through (maliciously) modifying bin/tar2fs
and waiting for it to be run; if mkimage-profiles
is installed system-wide as a package, the script
from /usr/share/mkimage-profiles will be tried so
those willing to allow vm/* build to themselves
can provide for a passwordless sudo (as described
in doc/vm.txt) to run a root-only writable script,
not user-writable.

Still not perfect but a step away from the abyss.