Also depending on how easily you can scale these semiconductors down, you may not need such complex cores. CPUs today are complex to (amongst other things) improve IPC - but if you’re really talking a 10^6 improvement in clock speed, I would guess that even a simple in-order core would perform better, and be much smaller.
DRAM latency will remain a problem, no way you can make CPU a million times faster without bringing in memory on the same chip. And you could probably only have a few kB close enough to the core to keep up in frequency.
Most probably you'd see this tech in highly specialized interfacing circuits, like current GaAs chips.
Fiber optic regeneration could benefit from faster electricals on longer shoots, you can only amplify so many times before the noise is amplified too much to ignore so they use optical to electrical to optical circuits. A much faster electrical path could make for some really cool high speed regeneration.
I can also imagine Juniper using them in an ASIC and charging a ton.
