Unix-based OSs won't stand still. To replace them we'd have to see a circumstance where it makes sense to start from scratch and rewrite everything vs. increme

Unix-based OSs won't stand still. To replace them we'd have to see a circumstance where it makes sense to start from scratch and rewrite everything vs. incrementally improve what's already there. I can't predict the future, but the market forces needed for some kind of new OS to make sense would have to be tremendous. As time passes and we build more and more on top of existing OSs it becomes less and less likely that we'll switch away from them because it will become more and more costly. Perhaps a state could create a unique OS as a hegemonic strategy. They could make people, companies and other states use it as a pre-condition of participating in their economic sphere. That could provide the incentive to use it even though it would take decades to catch up to existing OSs. China is the only one I can think of that could have a chance at this, though I still think the cost would be too high for them. North Korea would probably love to do it, but it seems unlikely they'd ever be in a position to influence other states to that degree.