Re: the gifted trojan device scenario, I think the primary line of defense would be to display a prominent boot time warning in the bootloader where a non-Apple

Re: the gifted trojan device scenario, I think the primary line of defense would be to display a prominent boot time warning in the bootloader where a non-Apple root of trust has been used, just as many Android devices do already -- perhaps similar to the recovery screen, but with more warning signs and an open lock symbol or something.