That said, the main hurdles seem to be managing people and funds, which government agencies seem pretty good at figuring out. So maybe not all that easy, but maybe not particularly hard either. The biggest problem might be keeping it secret, given the number of people that might need to be involved that are clandestinely working for a TLA but not as their main job and not steeped in the culture of secrecy.
E: ah, TIL. https://en.m.wikipedia.org/wiki/Rubber-hose_cryptanalysis
AT&T and Verizon don't have 'plant' employees. Much simpler - and legally, safer - to just give the bag of money straight to the corporation.
Risk of refusal. Risk of intentional or unintentional leaks.
As for other friendly and less-friendly nations, I'd be very surprised to learn that there weren't any other nations represented in the ranks of Intel engineers.
Yes, very unlikely. Something like the Intel Management Engine would be a much easier target.
The code is here: https://github.com/chipsec/chipsec
Wouldn't the malicious alterations introduced in a scenario like that most likely be exploitable defects that could be explained away as mistakes? If they accumulate too much around certain people that's suspicious of course, but it seems like it would often be difficult to downright prove that someone intentionally broke the security of a rather complex system.
This is a banal point, except: if the threat is that Intel (or some other huge vendor) backdoors their EFI binaries, it will get out that they did so. It's not "the perfect crime"; it's practically the opposite of that: one guaranteed to be detected, and that will exact maximal damage on the perpetrators when it gets out.