My reasoning was that the step needed to be non-reversible in order to duplicate the current behavior. However, after thinking over your suggestion, I haven't

My reasoning was that the step needed to be non-reversible in order to duplicate the current behavior. However, after thinking over your suggestion, I haven't come up with a scenario where that would be important. Ordinary users, even if they somehow experienced the temptation to disable remote updates, wouldn't have the expertise to act on it. And any malicious actor with physical access to the machine would have other more straightforward attack vectors (like USB vulns). So I think you're right -- and Intel has even less justification for hard-wiring the ME on by default.