It's precisely what Keynes meant. He meant that 15 hours of labor now will buy you what 40 would then. How could he have meant anything else?
How would he anticipate houses 50% larger than his generation's, or cars with twice the horsepower at four times the gas mileage, or universal air conditioning (as few houses in the US lack air conditioning now as lacked running water in 1950) or a monthly bill for Internet or proles being able to afford intercontinental flights more than once in a lifetime?
How would he anticipate houses 50% larger than his generation's, or cars with twice the horsepower at four times the gas mileage, or universal air conditioning (as few houses in the US lack air conditioning now as lacked running water in 1950) or a monthly bill for Internet or proles being able to afford intercontinental flights more than once in a lifetime?