@elly yeah so like, take mrchromebox. it's just edk2. take heads: it's just linux(and u-root). and they mostly only focus on newer stuff.
so a lot of coreboot distros will have very simple build systems, and configs that are mostly universal to all machines, actual coreboot config notwithstanding, and heads for example will have different kernel configs.
so libreboot's build system is designed to be very modular, and i'm ruthless about simplifying everything as much as possible all the time