> Capital will also be useless because the marginal value of everything will be driven towards zero

Capital is that fraction of produce set aside for future production. OpenAI is capital but not all wealth is capital. And capital isn't going anywhere - the machines will have gigafactories etc. The value of labor will plumet but present-day capital that is usable by the machines or can be scrapped and repurposed will retain value.

The value of square meter of land + mineral/sunlight rights (not capital) is likely to rise - the amount of wealth that somebody would give you for that asset would probably increase, as more wealth can be generated from it.

Individuals without wealth now will likely end up with a much lower allocation of those things which retain value (land, materials, etc) while having a much higher quantity (relative to now) of those things whose value will drop - AI tokens, electronics, entertainment, etc.

Essentially our current trajectory taken to the limit. Land expensive, food expensive, interest low, smartphone cheap.

> who will be the buyers

Imagine an impoverished and technologically backward country which has been colonized/occupied, and where the most valuable assets are exported well below market price or stolen. The people still trade their own labor for subsistence. They still produce some goods which have value in outside countries, they receive some charity, there is still tourism, their labor has some value (servitude, trafficking). AI would be the same (assuming laws hold up) - e.g. you could rent out your solar panels to OpenAI in exchange for a loaned domestic robot and a token subscription.