> Any manufacturer could put an eFuse in any of their hardware and lock it.

This is my point too, though. Do we trust Apple to not burn a hardware fuse if their community one-ups them? They've already done it on iPad and iPhone hardware when users find a boot ROM exploit. All that they'd need to do is push an update for "security" purposes, and then the new boot flow could refuse to boot into unsigned volumes or deny running unsigned bootloaders. There would be no way to downgrade.

This is basic ARM security architecture stuff, I'm a little shocked that people can't imagine how this type of lockout is possible. There are tons of commodity ARM boards that are effectively bricked and eFused to user-hostile security epochs.