DragonFly is getting support for running a virtual kernel multi-threaded, i.e. a SMP virtual kernel. A virtual kernel is a userland process (like running any other application) that runs a whole kernel. It's especially suited to make kernel programming life much easier, because you can now test a new kernel within seconds while you don't have to reboot your machine where you are working on.
I think this is required to ease Matt's work on the new HammerFS clustered file system.