This looks very good.

How can packages be added? How can it be reconfigured? How is one supposed to add management tools (think libvirt, openstack) to it?

I took it for a spin and noticed it had kvm, a whole lot of regular Illumos binaries and that it had a BSD-ish userland.

I couldn't find anything like libvirtd, I didn't get to check if it has it, though.