I must have expressed myself unclearly. (First though: Windows now supports full disk encryption and secure boot. It certainly did not when I and it parted way

I must have expressed myself unclearly. (First though: Windows now supports full disk encryption and secure boot. It certainly did not when I and it parted ways back in the days of XP SP1 circa 2002.) I was not implying that the secure pass phrase/secure boot/etc be considered the basis for a secure mobile OS. Much the contrary. Multi-user systems with privilege hierarchies are fundamental aspects of how we now architect even our single-user devices. (Discussing whether another system is possible, desirable, and/or whether we could have or will eventually go down that route is midway between hypothetical and counter-factual.)