http://lists.squeakfoundation.org/pipermail/vm-dev/2022-April/037922.html
As I said before, this is also a good solution for Cuis. So, my suggestion, is to simply make primitive 126 fail on MacOs.
This wouldn't affect older images checking for the platform (as you say, for a performance improvement), but would fix older "untweaked" images, solving any concern about strict back compatibility for the VM.