Power will always scale linearly with cores, of course, but you could make cores less power-hungry with reversible computing: https://en.wikipedia.org/wiki/Reversible_computing

Actually useful reversible logic is, as they say, an open problem.

My point was that a new transistor shrink would give you lower power vs. the same transistor in previously larger node. You get more compute-per-watt with small transistors. If scaling stops, then all kinds of things get more difficult.

I have heard that Electrons move about a millimeter second (although electromagnetic emanations propagate at the speed of light). This is allegedly the benefit of 'optical' computing.

Not quite.[1] Propagation in most interconnects is about half the speed of light, because real-world wires have capacitance. (As low as 25% for CAT 5 cable, as high as 90% for open-wire antenna feeds.) Optical fiber runs about 70% of the speed of light. On-chip interconnects run 30%-60% of the speed of light. So there's some propagation delay improvement with optical interconnects, but it's a factor of about 2, not some huge improvement.

[1] http://www.edn.com/electronics-blogs/all-aboard-/4426188/Rul...