A nit: I would think that the PKG_MAKE_JOBS or PKG_BUILD_JOBS variable would apply equally to the install phase, and might also apply to core usage in pigz in package creation, and some future parallelization of wrapper generation and patching. I see MAKE as sort of a phrase for the interface and that other build systems are basically implementing that interface. Given that we have MAKE_JOBS, I'd just as soon stick with the language. Overall I did not have any negative reactions to your proposals.
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