To me things that are worth starting over would be the CPUs that we no longer understand and the OSes that are debugged into existence. Not a computer that has no SSD because memory is persistent.
I'd wish physics would end at Newtonian mechanics and Maxwell equations, but alas special- and general relativity cannot be avoided in some circumstances and neither can quantum mechanics in others.
The same is true for CPUs and operating systems - if you need high performance and the ability to do real-time high-resolution media playback, digital content creation, high-bandwidth networking, high-colour and high-resolution graphic displays with font smoothing, auto-scaling, multi-monitor support, pluggable peripherals, etc. etc. you'll get complexity.
There's only so much that can be achieved with simple TTL and core memory...
Microkernels and provably correct OSes are great and available, too. But things start to get messy quick once you add support for various protocols, devices, and capabilities. Not just because it gets harder and harder to do, but also because there's diminishing returns: the vast majority of users aren't OS developers and just don't care.
The same way the vast majority of people don't care about the layout, build quality, and logical soundness of the plumbing in their homes (as long as it works sufficiently well) or the technical details of their refrigerator.
That's why there's very little incentive to build small, "clean", and provably correct OSes for the general public. You will find them, though, and they are in use.