As it seems, there is nothing to prevent us running several libvirt instances — except of hardcoded pathes to the libvirt socket, images directory and so on.
Keeping in mind libvirt driver lock (https://bugzilla.redhat.com/show_bug.cgi?id=856609), it is a serious limitation of libvirt scalability: there is no use of several CPU while creating VMs (and, maybe, not only creating, but we stuck on this with creating).
It would be nice to make such pathes configurable (with default values == what it uses right now). I will allow us to run several libvirtd instances w/o usage of FS namespaces, that is not too trivial.
The libvirt design is such that there is 1 instance of libvirt which runs privilege, and optionally 1 instance per non-root user account which run unprivileged. Running multiple privileged libvirtd instances is a non-goal.
What is your use case for having multiple privileges instances of libvirtd ?
There is a scalability issue with libvirt on hosts with many CPUs, caused by the driver lock (see bz#856609). It can be solved either on the driver level, or with several libvirtd instances. The former is the better, but one doesn't exclude another.