Volume? Not yet...

True.

My point was just that if you're only concerned with PHYSICAL limitations, like lightspeed,
then the limit is a volume, and not an area.

I agree with you we are nowhere near being technically capable of designing and manufacturing
a true 3d cpu (one that uses the entire volume of say a 1000mm3 to do computation)

But this is a technical limitation, and one that can, atleast in principle, be overcome. And
not a physical one that asfar as we know is final -- like lightspeed.