Fair. Yet something as core as an OS should be planned to be OS'ed once you don't want to maintain it. Even just the fact that it's non trivial and large would

Fair. Yet something as core as an OS should be planned to be OS'ed once you don't want to maintain it. Even just the fact that it's non trivial and large would justify to structure code for new joiners. Large tech companies all try to pass as green nowadays, yet consider the waste that throwing away code that would likely interest others represents - even after two decades of service.