Once we have virt-clone'd a running VM instance to an instance named e.g. "vm-backup" there is no easy way to virt-clone the same VM instance to the same "vm-backup" instance because virt-clone complains that "vm-backup" already exists. Such a feature would be very useful though, to regularly backup a running VM instance. Right now, the workaround method is to virsh undefine the "vm-backup" instance before virt-clone-ing to to it again. So a virt-clone --replace flag would be very handy.
I imagine we'd actually implement this by explicit storage snapshot capabilities - e.g. if you could create a snapshot of the VM (rather than cloning it) and later revert the VM to the snapshot Anyway, this is an RFE - moving to upstream bug tracker for now
Upstream now: http://git.fedorahosted.org/git?p=python-virtinst.git;a=commit;h=b8c02a834024e251bab58d4f0904fbef5b357899