The power button on my current work laptop (Microsoft Surface 4) is integrated into the keyboard to the left of the delete button rather than being a separate button outside the keyboard like every other laptop I've ever used. If you're a bit clutzy you can easily put the laptop into sleep mode when intending to hit delete, pic below (not my laptop but keyboard layout is identical).
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My MSI places the power button as the last key on the function row, now as for accidentally touching it it's not an issue as a short/quick press does nothing and needs to be pressed for ~4 seconds to bring up the shutdown swipe screen. The one issue is that if the keyboard is not present or stops working then you can't turn it on, something that was nearly an issue for me as a water spill means half the keyboard doesn't work, luckily that button is one that does.
Also with it being a touchscreen laptop that can be flipped you end up with no usable power button if it is flipped, annoying if it goes to sleep when it is flipped and you have to shut it and reopen it to turn it back on, my other two similar laptops (a Dell and Asus) had the power button on the side.
And from my keyboard playing background, 3.5mm MIDI connections, 5 pin connectors are not that large and there are already standards for using PS/2 mini dins instead, whereas there are two standards for 3.5mm jack connectors.