b) From: https://www.aspeninstitute.org/wp-content/uploads/files/cont...
> I would predict that the standard of life in progressive countries one hundred years hence will be between four and eight times as high as it is.
Note the qualification "in progressive countries"; have we any?
c) I've heard that the ratio between the cost of nails and the price of lettuce is still more or less the same as it was in the 1770s; the big difference is that in the 2020s a "yeoman farmer" doesn't want to buy nails with their market goods, but wants to buy cars and smartphones.
d) Finally, on the parochial basis that my life revolves around informatics, we've vastly exceeded the 4-8 times Keynes actually predicted.
His future is here — it's just not evenly distributed.
Lagniappe: https://www.smbc-comics.com/comics/1729266273-20241018.png