In section 17.3, Keynes sees to be illustrating how one could generalize beyond the money rate of interest, namely beyond money as the unit (or “rent factor”) by which interest rates are measured. He talks about how one could conceive of interest rates in terms of other commodities, e.g. wheat or horses (see Chapter 17, Section II), and then goes on distinguish money as a privileged or special case, owing to certain unique characteristics money has which these other commodities lack (see Chapter 17, Section III).
He then suggests that if our interest rates we instead measured in other commodities (i.e. commodities which lack the special characteristics of money, such as how its utility is its exchange value, and how increased demand for money does not have the conventional effect of prompting an increase in supply), it may result in an arrangement whereby the “rates of interest would only reach equilibrium when there is full employment.”