I think your understanding of capitalism is limited. Before capitalism people sold things based on 'exchange-value', the cost of a good or service.

Capitalism creates 'surplus-value' which allows a good or service to be assessed as 'debt' without having to sell it to assign value. A practical example is real estate where debt in the forms of loans are taken out on a property. Debt assigns 'surplus-value' to the property. The property owner doesn't need to sell the property to know how much it is valued for.

The reason capitalism is 'sustainable' is because the value of real estate and other commodities increase in value. Debt is the assigning of value to something that is not 'liquid'. The reason capitalism is 'unsustainable' is at some point property values (and other debt based commodities) far exceed the ability for working people to buy them. Wages are 'exchange-value' and may not increase while debt is 'surplus-value' and always increasing.

So the question, (or next evolution beyond capitalism), would be how to assign 'value' without the need to assign 'surplus-value' through debt?