> How about actual switch covers (and switches that are not located right in the same area as stuff you are using routinely) instead of a glorified detent? Though I suspect this would also succumb to muscle memory

The switches are already pretty distinct - but that only reduces failures, it can never eliminate them entirely.

> Or (at the cost of complexity) you could interlock with the throttle lever so that you can't flip the cutoff if the lever isn't at idle

More complexity also means more failure modes. You don't want it to be impossible to shut down the engines due to a broken throttle sensor.