I think people are putting to much stock in 3d stacking. Heat dissipation problems with 3d stacking are even worse then that of die shrinks reducing area to shed heat.
At most you will see Interposer with a CPU and GPU on top plus maybe memory on top of that, but I'm skeptical if we will even see that in any wide spread use. I think everything will just be laid out 2.5d style on a interposer and thats the most we will see.
And SMT-4 isn't happening. It actually incurs a rather substantial area penalty, were talking 20% or so area of the chip to do it right, at least on both Sun and IBMs SMT-4 chips.