If only workers would form some kind of a community, which would take monthly contributions and that would then be used to upskill. It would unite most, if not all people in the same industry.
Local IBEW halls have apprentice programs (JATC is an common name for this program) where the apprentices go to class at the union hall one day a week for 20 weeks a year and spend the rest of the time working in the field.
I am pretty sure that sheet metal workers, pipefitters, and plumbers unions offer similar programs.
> - Having a shop in China machine the parts for you can be quite acceptable, especially in higher volumes
Yes, in some circumstances, your idea can work. To a degree. But there are plenty of trades and whole industries where domestic employment has fallen by 100X or more, because global capitalism found plenty of cheap workers in distant countries. Where 10X (or more) lower pay didn't seem so bad, compared to their local alternatives.
Sure then that expertise could migrate to other countries, possibly some in Africa. But the demographics slow down is probably already going to afflict those countries before the expertise leaves east asia in the first place.
I truly believe that within 40 years we are going to have a massive infrastructure maintenance problem, where the world will run dry of trained professionals to maintain everything that is already built. And, like I mentioned above, the wealth inequality will reduce because the owners of capital will need to pay premium rates for qualified workforce (think how cobol is today).