The article suggests a “simple, well-labeled rotary control ... would accomplish the same function” as a power button and “prevent the user from accidentally activating the control in a way that is no longer hidden”. But a rotary control itself has a serious problem, in that it can mislead the user as to the state, on or off. If the power has failed and the machine does not restart when it comes back, the rotary control will remain in the ON state when the machine is off. From memory, Donald Norman called this kind of thing “false affordance” and gave the example of a door that needed to be pulled having a push-plate on it.
So my iMac, among many other devices like the light I wear on my head camping, has a button which you long-press to turn on. It is a very common pattern which most people will have come across, and it’s reasonable to expect people to learn it. The buttons are even labelled with an ISO standard symbol which you are expected to know.
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