It's unrealistic to expect any increase like this (productivity, GDP, the stock market, Etc.) to remain in a constant increase - even if the increase was linear. Certainly not a exponential curve.

It's simply not a realistic possibility, both theoretically nor from the last few hundred years of observations.

The increases in productivity quoted in your article come during times of extreme change (I.e. agrarian to industrial ages.) Similarly for the industrial to information ages (computing.) In between both there was a flattening in the curve of the increase.

Also , many of the increases in productivity during the last few decades (I.e. during those flattening of the curves that derived form technological advances) came from increasing pressures on employees - which has already reached an untenable social tipping point.

Until another dramatic change in technology creates another boon in production (perhaps AI?) it's simply unrealistic to assume the "productivity curve) will continue to increase as it has been.