Well, the biggest problem is that Operating Systems need a common interface to share software/application/service support, generally. Allowing a 'Cambrian Explosion' of Operating Systems would present a problem where we don't have common software, and everyone's development efforts are strewn all over the place. What you're really describing is the world of alternative Operating Systems, of which there are many cool things to check out (Fedora Silverblue, HaikuOS, Free/Open/NetBSD, etc.) Most of these platforms share a degree of API support (however faint that support may be), which allows them to try extremely experimental things while retaining a large amount of software support.<p>If your question is "what do mutations/evolutions of modern OSes look like", look at the ongoing friendly competition between Guix and NixOS. Both OSes have radical features like declarative configuration and generational base systems, but they go about implementing them in different ways. Two species of the same genus, two families with similar religions. Similarly, the BSDs have a lot of cool things that completely stray from Unix/Linux spec, and their own strange internal conflicts/rivalries.