Unfortunately with clock speeds, we wind up bumping up against fundamental laws of physics.
At 10Ghz, something moving at the speed of light can only go around 3 centimeters per clock cycle. Take out gate delays, and you wind up with something that just isn't practical.
Speed of light delays don't have anything to do with it, since features sizes are also shrinking. If we were limited by that then shrinking transistors from 65nm to 22nm should have let us clock equivalent cores three times as fast, but that didn't happen.
The important things that changed were that smaller cores tend to leak more, which means that voltage had to be scaled down aggressively. And drive currents are now limited by velocity saturation.
IBM and the Designers of the POWER6 cores went all the way up to 6 GHz and had them operational. The current POWER7 chips can go up to 4.25 Ghz and they have something like 32 Threads per chip
The T2 processors from Sun had over 100 threads per chip. Its a shame that they didn't do better in the market place.
T2s were pretty slow tho, we tried running ruby on them and they couldn't do it. Even with Java it was pretty mediocro performance. A dual core intel could kill a 120 thread sun box by a large margin
Take eight chips. Stack them, insert spacers and bridges from top to bottom, and connect them via BGA or pins or what-have-you on the very top and very bottom chips.
Now turn them sideways, so they rest on the edges. Put the stack in a small ceramic container with copper bottom and top. Fill with a high efficiency thermal transfer fluid, and make sure the convection currents flow properly.
You're right about bumping up against the fundamental laws of physics, but 10 GHz is still on the low side. For single transistors, see HEMTs. They can run an order of magnitude faster than that. Whole chips are something different, but I wouldn't discount it just yet. 10GHz on silicon though.. that's doubtful.
At 10Ghz, something moving at the speed of light can only go around 3 centimeters per clock cycle. Take out gate delays, and you wind up with something that just isn't practical.