(For instance: this includes Apple phones, or you would have mentioned them, the way you did Pixel, right?)
It's also a common phrase to say “kill the engine” even if that means just turning the ignition off in the usual way, and again, it doesn't imply damaging the engine.
The kind of switch you're describing would be useful but calling it a kill switch would be confusing to US-English speakers.
If that's the case so we have a real hardware kill switch, then ladies and gentlemen the above image is the best possible ad for the PinePhone. Forget stock photos of pretty models, athletes or busy professionals, that is what privacy sensitive people want to see on the back of their phone.
I didn't look at the phone architecture yet, so I was referring to chips mapped on the MCU bus lines since the chip enable was mentioned. USB peripherals would be very different, still interesting if they both used USB for ease of support and directly drive the CE lines to be sure the chip is being disabled.