Comment by kristjank

I wouldn't. Spinning things around is a really trivial thing to do and we've perfected it since the invention of the wheel. More relevant to this issue, synchronous machines also interface with three-phase (or any other AC) power systems really well. Supercapacitors may become dramatically more efficient in the future, but they inescapably require more semiconductor technology to get from DC to AC, which reintroduces the semiconductor peak load problem.