The situation of you only able to produce wheat strikes me as more equivalent to the situation of supporting people who are incapable of supporting themselves. A more realistic comparator to your hypothetical person who can only produce wheat is, say, someone in the post-traumatic amnesia stage of a severe brain injury who can’t produce anything. The only answers I have heard for that situation are charity or government provision of a basic income.
As a practical matter, I can’t think of a single case where a real human being can produce wheat but not anything else.

Its certainly not crazy to think that it may result in a lasting or growing relative disadvantage to sellers of labor, but if production gets cheaper that relative disadvantage can still be with an absolute advantage as you get a smaller portion of a bigger pie, and your piece still is larger even if its grown only half, or even only a millionth as much as some others.

Also people, esp. over the long term, respond to such changes and incentives in complex ways. Even just in terms of voluntary economics people will learn new ways to be useful to those with wealth. Also you have the possibility for political redistribution.

1. Utility curves. We know that above (approx) $15K a year, increases in income yield little increase in happiness. So those “luxury” goods are less valuable, meaning producers can’t sell them for enough (in aggregate) to make a living.

2. The remarkable efficiency of technology-driven corporate capitalism is also a remarkably efficient pump pushing wealth to the top. With high enough productivity (one person with a computer making everything?), this could overwhelm the price cuts that people down the ladder experience.

3. The massive productivity gains of recent centuries have been accompanied by massive increases in government redistribution. There’s not one thriving, prosperous country that doesn’t have a mongo huge dose of it.

Is it possible that that redistribution is necessary to maintain aggregate demand so a high-productivity economy can thrive and prosper?

Why Prosperity Requires a Welfare State

In Victorian England, there was a widely understood principle that the equilibrium wage of the working class was the wage that kept the working population constant (the “Iron Law of Wages”). If pay goes down from that level, malnutrition and disease kills workers. The labor supply therefore falls and wages rise. The reverse takes more time, as children take time to grow.

So far, this insight has not seemed relevant to North America, because the continent has been relatively unpopulated. Of course, the population keeps growing.