Also, adding something like that would be an incredible amount of work. Basically you would have to totally re-do the layout even if you're just adding a macro somewhere and totally re-design it if you're not going to end up causing a drastic decrease in max clock rate. That's for an management engine or tracking style thing. A backdoor that makes #5F0A40A3 equal to every other number for password bypass wouldn't be that invasive and might only slow things down by a little bit so I guess that's a possibility if a certain design becomes really popular?