…i’m absolutely ignorant of its current state, but every time i’ve checked in on progress of GNU/hurd over the past three decades, it still hasn’t matured into a stable production-ready platform: i’m not sure if that’s an artifact of technical viability or developer interest…
…NeXTstep was built on mach and, although i’m unsure if any antecedents remain in macOS, it was certainly production-ready in its day; i remember a couple of decades ago there were stopgap versions of the HURD built on top of mach instead of their own microkernel but i thought that was only ever intended as a temporary workaround…
…i presume on that basis that sustained developer interest was its greatest hurdle, no pun intended…
edit: …is this the post-mortem you mentioned?..