the siesmic impact of that decision has been kind of lost - iphone etc. all happened because of the moment in time Steve J and others took that decision

I mean, what would have prevented NeXTSTEP from being developed at Apple?

Backward compatibility or them thinking too alike to have come up with something so different. Plus, they might have bought BeOS. That would've been awesome. We'd have gotten multicore benefits way earlier. Mac OS X server might have also succeeded more given concurrency benefits.

The minds behind NeXT weren't at Apple, Jobs was not alone in this startup.

It was the team work of all these people together that brought NeXTSTEP to life.

You cannot ignore the human aspect of it.

Also Apple never was a UNIX shop, A/UX was just a distraction they never cared much about.