I'm creating a startup to do just that. There's both huge upside[$$$], but also some legal risk. If this appeals to you and you're an innovator in the social engineering space lmk.
Are there rules/standards for how these top secret keys are stored? HDCP, Mediavine, keys to the Internet, etc. Sure, you could keep it locked in a Scrooge McDuck security vault, but you need to be able to burn the key into hardware/software, meaning it ultimately needs to be distributed across many machines, greatly increasing the number of people with potential access.
There's both. The encryption (decryption) key has leaked. The original question was about "making your own microcode", for which you would need the (not leaked, and unlikely to leak) private signing key.
Those codes were intentionally zeroed to get around what was (most likely rightly so) considered to be a failure of the launch doctrine to take into account the possibility of the leadership being knocked out which would make a retaliatory launch impossible due to the lack of valid launch codes.
I don't think Intel has such problems and I assume they are keen on keeping their microcode update process from being abused - it is not as if they don't have enough problems as it is.