You've never been able to run a virtualization product inside a virtual machine, I don't think Hyper-V changes that.

If MS designed Win8 to load the Hyper-V as part of the boot-up sequence for the OOBE setup wizard, that's rather stupid. In fact, I'd be surprised if it's loaded by default, because at least on Server 2008 enabling it has some pretty big performance implications for the host OS.