Yes, but your diameter can shrink significantly if you have more than a single plane of thickness. Currently the thickness of the die is less than 1% of the typ

Yes, but your diameter can shrink significantly if you have more than a single plane of thickness. Currently the thickness of the die is less than 1% of the typical diameter, so that 2/3 -> 3/4 increase is negligible compared to the >100x decrease in diameter for the same number of transistors. The biggest issue (IMO) will be heat dissipation and manufacturing time.