We might have already crossed the line where the cost per transistor goes up when transistors get smaller, which may put an end to transistor shrinkage before it becomes impossible to make smaller transistor. Expensive 40-series CPUs from NVIDIA may be the harbinger of this trend.

The industry has directions to go. Other semiconductors such as Indium Phosphide can run a lot faster than Silicon, looking at SBIRs that have been funded it seems possible that 50 GHz+ processors have been made. The other one is devices that are stacked 3-dimensionally and have a huge number of parts but the parts might run a lot slower than current processors to control heat production.