Right, I'm not suggesting that it's even remotely possible for millions of systems to be updated at the same instant, just that outside of some special circumst

Right, I'm not suggesting that it's even remotely possible for millions of systems to be updated at the same instant, just that outside of some special circumstances like beta channels (yes Google Play supports this) the huge numbers of devices are offered the same updates. If trust is lost in the update mechanisms then something will be done to restore it. That would likely be large developers like Apple, Microsoft and Google deploying a technical solution to prevent themselves from sending different updates to different devices without loudly warning the user and automatically reporting the attack to the world. That would please users and reduce compliance costs. Really, the major operating systems should just do it now to prevent this from becoming a problem in the first place.