Legal question: if you had whole-disk encryption, and the duress password just zeroized the decryption key, would that be "destroying evidence?" Especially if there was a recovery possible but not instantly available, such as a Yubikey in a safe deposit box in a bank. That would take a subpoena to get, and there is an opportunity to challenge the subpoena in court first. Not instantly at the border.
Something like that should be a standard feature of a secure phone.
Something like that should be a standard feature of a secure phone.