As mentioned in a sibling you still have the hypercalls, and you definitely need those to still be present if you're running at ring 0 since, essentially, direct access to the hardware is probably an opportunity to attack the whole physical system (since hardware often has arbitrary bus access). Never mind the need to arbitrate access between multiple VMs.
And this is what I mean when I say that taken to its conclusion you're just reinventing processes.
I think this kind of performance claim needs to be solidly proven by something at least vaguely like a real running application to be taken as a given.
