Physics is still a problem there as well. 1 THz = 10^12 Hz. The speed of light is ~3E10 m/s so at 1 THz light can only move ~0.0003 m/cyc = 300 um/cyc. Electric current moves slightly slower than the speed of light through copper and silicon but its close enough to approximate here. That means in a CPU running at 1 THz it would take multiple clock cycles for a signal to move from one side of the CPU to the other. You also have to take into account the switching speed of transistors and the distance from the CPU to memory. All together, you would just end up wasting a lot of clock cycles achieving nothing and driving the current required to run a CPU at those speeds would generate a lot of heat.

Comes down to another issue discussed in the article: extremely high power and current density, which require another greal deal of engineering to cool down and make sure things don't vaporize, melt or simply break down.

I’m just speculating. Theoretically if you have vacuum sealed CPU, it could work. This brings other problems. How would you remove heat released by the chips in vacuum if there is no airflow.