The proposed metric, a product of population and incomes, is unbounded (in aggregate). Population isn’t. But nominal incomes, a function of the unbounded money supply, is. Real incomes are trickier, but they--too--are unbounded. It just requires some fraction of the basket be immaterial. As long as that component grows sufficiently, the real value of the basket–which, again, is subjective–grows.

This isn't some edge-case philosophy, but a well-recognized effect of the subjective nature of value. (The physicist in me points out that the observable universe has, based on known physics, a finite computational capacity, but that objection merely illustrates the absurdity of proposing a practical upper bound on growth.)

We're used to thinking of production as making cars and ships. Those activities represent a falling share of human activity (weighted by value). To illustrate, witness the falling material intensity and energy intensity of GDP growth.