Manufacturing is slowly moving to be "on demand". That is, a consumer purchases something, then it is built and shipped to them. It doesn't make sense any more for a company to predict market volume and then produce goods to match the prediction, especially since technology turns over so fast.

With that in mind, I could see Apple having simple components being produced in a number of different countries, then shipped out to wherever their products are in demand. Then the components are assembled by robots locally and the final product is picked up or shipped down the street to the consumer. I remember reading that this is where the auto industry is heading. They want to produce interchangeable car parts which get assembled at the dealership when a person purchases the car.

So to your point, China is already done. Instead of huge factories producing consumer ready goods, Apple just needs a handful of smaller factories making much simpler intermediary components. It's much easier to setup and move these smaller factories around, rather than these huge factory cities managing a massive production line.