When it's more close to inclusion, I'd also post it to main qemu list. 
But right now, I'm just aiming at a first round around this draft.

The attached patch is enough to make the notifications DEVICE_CHECK and 
EJECT reach the kernel. As far as I understand, some userspace black 
magic that keeps changing its scroll is needed to really put the 
processors logically off/on after the notify (acpi code itself will 
never call cpu_up/down)

Just let me tell you what you think.