I am confused by the way the Economist phrased Mr. Rognlie's argument. The crux of Piketty's argument is that when global returns on wealth (r) is more than global economy growth (g), capital will start snowballing into the hands of the few very quickly.

The mechanism of r getting bigger than g is not an increase in r, but a decrease in g. The increase of the global economy is dominated not by increasing technological efficiency, but by population growth. There is an upper limit of the number of people we can fit on this rock (whether 9 billion or 100 billion, we will hit a limit at some point). Once we bump into that ceiling, growth will slow dramatically, and those who have already managed to create a sizable stash, or who have the talent to regularly beat the market, can accumulate wealth to no end.

In short, as I understood Piketty's book, the fact that r might not increase if we put the right limits on housing development, doesn't change the overall hypothesis made by Piketty.