It's a happy accident that when Jobs returned to Apple, he brought the NeXT OS stack with him and had Apple stick a decent GUI on the front end that turned into OSX.
The accident is that they were desperate and would have bought any decent OS they could to replace the gigantic failure Copland was. NeXT had the one with the more eloquent salesman and the only person who could have given back any semblance of credibility to Apple's lineup.
Were NeXT based on VMS, Amiga, TOS, MP/M or anything like it, that would be OSXs base.
You said it jokingly, but I think this x86 world where the OS-space seems divided between a bastard child of VMS and variants of Unix is unbelievably boring.
Years ago in my undergrad I took a most excellent OS course offered by the indomitable Peter Denning. As presented, his course basically considered each part of an OS, chose the best of alternatives for core system concepts, and built the OS from there. The result was something not grossly unlike a modern nix, but still leaving enough wiggle room for the large number of variants we see today.
His comparisons between the way these concepts were instantiated in an nix and in other OSs were particularly good (and scathing).
That being said, it is a pity that there aren't still a dozen or so major OSes out there, each coming from a completely different approach, oh the days when an Amiga or a BeBox were interesting consumer choices. You can still find lots of minor OS variants around, but they are very small communities and it's really all boiled down to a very small and "boring" handful.
Additionally, most new OS approaches suffer from a distinct lack of software. And slowly but surely we find the inevitable creep of software Ports into new OSs, using bringing *nix like infrastructure in with them.
