"Becoming viable" does not mean "automatically put into execution". You still need to take overall demand in account.
Consider this: if demand was not a factor, anyone living in a moderately wealthy country would be practicing labor arbitrage and sending money to poorer places. Ask yourself why this doesn't happen.
1) corporations moved manufacturing to where labor was cheap, but brought back the goods to sell them. This only works for as long as there is healhy consumer market somewhere. If AI really gets to automate most white-collar work, there will be no healthy consumer market left anywhere around the world.
2) The essay touches on this: any of the previous offshoring / job displacement movements happened on a much longer timeframe than what is being pushed now by the powers that be.
In a world where it’s dramatically cheaper to build infrastructure like roads, power, and plumbing, lots more land becomes desirable as a place to live.
Take Phoenix, for example, once air conditioning became cheap and pervasive.
> where subways cost 1/20th of what they do today.
1) We are talking about reducing the cost of labor, not overall costs.
2) Your logic only applies in the micro, not on the macro. If the cost of producing one thing goes down while population keeps their purchasing power, then what you are saying would make sense. The whole point of the article is that accelerated automation can bring a scenario where the cost of producing "things" would go down, but the economically active population would shrink drastically.