What if Intel and AMD speed up the processor speeds after 2000s
If they could, they would have. Believe me. There are fundamental problems with increasing clock speed beyond where we are (smaller transistors mean higher voltage gradients for a given voltage, so you need to drop the voltage, which means dropping speed). Also, keeping the same switching rate with smaller geometries means higher heat production per unit area.
Basically, they've hit a really steep curve on clock speed. There's not much they can do about it with any realistic known technology.
SO....
to get them to keep increasing clock speed, you have to get significant new technologies in place. In which case, the clock speeds may be the least of the differences.
Edit: you might be able to double top clockspeeds by immersing the processors in liquid nitrogen - but then you have to worry about all the other components that don't want to be that cold. And running a nitrogen liquification plant just for your computer isn't going to be popular....