Indeed; I read this specifically because I was curious specifically what MacCarthy's requirements or specifications would have been for such a thing, back in 1964. I.e. the young MacCarthy take on the problem and how it reveals his thinking about such a thing.

What it reveals is that he had a very firm grasp on advanced computer and operating system architecture. He describes the requirements for an interrupt-driven concurrent system which has two levels of protection: a user and executive mode. Moreover, he recommends a small, well-debugged kernel be used, architected in such a way that errors in other pieces such as peripheral drivers, are recoverable. It's almost as if he's hinting at a micro-kernel architecture.