Probably not, but who would have access to this kill switch/phone bricker? The customer with a private key? (...with no way it could be activated by the phone

Probably not, but who would have access to this kill switch/phone bricker? The customer with a private key? (...with no way it could be activated by the phone manufacture/service provider/legally forced by governments.) Probably not, because it's not user friendly enough, or some excuse. It's a problem that needs solving so we actually own and control our property.