But let's think in a wider scope (disclaimer: this is not my idea, I remember reading about it a long time ago): what if a certain cryptographic "magic code" at the beginning of a memory page would trigger the execution of arbitrary code embedded in that page?

Such a thing could be triggered over the network, wireless through bluetooth/wifi, or by specially crafted images on a webpage, or whatever creative technique you can think of. It'd effectively give the govt instant root access to any device with the affected CPUs.