My theory is that the max output of the average worker has been eclipsed by an order of magnitude by people who can communicate with the 21st century machines. i.e programmers. Programmers are just modern day factory workers. They are leveraging their natural ability to produce more with machines. Unfortunately society hasn't realized that programming is a core skill, like math and english.

Until everyone knows how to leverage their output with programming expect the gap between the upper middle class and everyone below to grow.

If you're currently in the upper middle class and above and you are not leveraging software either directly in your role or as an manager / owner, then you're at risk of falling in class.

When the industrial revolution started, factory workers were paid very well, relative to other workers (i.e agriculture). Once society realized that math / english was a core skill required to live in the new world, factory workers as a group grew and became the middle class. I expect the same thing to happen with programmers if we as a society get our shit together and educate our population correctly.