Note added later: Some people have pointed out online that if MINIX had a GPL license, Intel might not have used it since then it would have had to publish the modifications to the code. Maybe yes, maybe no, but the modifications were no doubt technical issues involving which mode processes run in, etc. My understanding, however, is that the small size and modular microkernel structure were the primary attractions. Many people (including me) don't like the idea of an all-powerful management engine in there at all (since it is a possible security hole and a dangerous idea in the first place), but that is Intel's business decision and a separate issue from the code it runs. A company as big as Intel could obviously write its own OS if it had to. My point is that big companies with lots of resources and expertise sometimes use microkernels, especially in embedded systems. The L4 microkernel has been running inside smartphone chips for years. I certainly hope Intel did thorough security hardening and testing before deploying the chip, since apparently an older version of MINIX was used. Older versions were primarily for education and newer ones were for high availability. Military-grade security was never a goal.
Second note added later: The online discussion got completely sidetracked from my original points as noted above. For the record, I would like to state that when Intel contacted me, they didn't say what they were working on. Companies rarely talk about future products without NDAs. I figured it was a new Ethernet chip or graphics chip or something like that. If I had suspected they might be building a spy engine, I certainly wouldn't have cooperated, even though all they wanted was reducing the memory footprint (= chip area for them). I think creating George Orwell's 1984 is an extremely bad idea, even if Orwell was off by about 30 years. People should have complete control over their own computers, not Intel and not the government. In the U.S. the Fourth Amendment makes it very clear that the government is forbidden from searching anyone's property without a search warrant. Many other countries have privacy laws that are in the same spirit. Putting a possible spy in every computer is a terrible development.
Source: https://www.cs.vu.nl/~ast/intel/