I didn't suggest it would be physically harder than stopping nuclear proliferation. I suggested it would be politically harder. The success of the scheme "depends on whether the ones doing it are also the ones making the laws", and that means it depends on international politics.

Nuclear proliferation is a very, very bad analogy for your proposal because the NPT imposed no controls on any of the five countries that were already making nuclear weapons at the time the treaty was adopted, who between them were militarily dominant throughout the Earth. It was in the immediate self-interest of the five nuclear powers to organize a cartel on nuclear weapons, and they had the means to enforce one, too. Further, of the countries best situated to defect many were already getting the benefit of having virtually their own nuclear weapons without the expense of their own R&D programs through the NATO Nuclear Sharing program.

On the other hand, organizing to end Moore's Law is to the immediate disadvantage of any country that signs on (much like agreeing to cuts in carbon emissions), and even any country that simply wants to buy better computers. The utterly predictable result is not a world consensus with a handful of rogue nations trying to build fabs in the dark lest they get bombed by the US. Rather, it's the major current manufacturers of semiconductors never agreeing to end R&D and implementation. And then even if they do, a country like the People's Republic of China blowing off the existential risk, then going ahead with its own domestic efforts.