I could imagine this being very useful in the form of a tool like debootstrap(8), intended for conformance fuzz-testing. Feed it a set of switches/enum values, and it'll install these various different odd technically-conformant things into a chroot for you, in any combination you like. Feed it a random seed instead, and it'll select the setup flags based on seeded PRNG output.

Now, set up your CI system so that your "POSIX build" builds N times, each time in a new one of these randomly-generated "technically POSIX" chroots.