Though my vision for IoT goes beyond simple energy-efficiency, because it is the same old story – you can be very efficient in perfect conditions (narrow band of power supply).
Instead, it should be about operating in a wide dynamic power range. Therefore energy-modulated computing is a way. Scoop some energy from the environment and drive your logic from a cap! There maybe nothing left for computation if you start to apply smart power regulation. As we say in Russian – “ne do gribov” (no chance for luxury)!