We may be on the verge of the next processing breakthrough. The reason (as I understand it) that we’ve been essentially stuck at the 3GHz line is due to our reaching the practical limit of silicon’s insulation abilities.
The reason we’ve been stuck at 3 GHz is because of many chip designers being lazy on circuits and layout. In the past, they got speedups for free thanks to scaling. Now they have to work for it, and they just want to take the easier - but incomplete - path of parallelism instead.