If — and it's a big if because civil infrastructure is a lot more than just domiciles and a bit of tarmac to travel on — it were done right, the metro areas could expand. And many have, which is why we're increasingly urban as a species.

Sure, still technically finite, but even just at the Netherlands' population density, we could fit the world population into 1/10th of the world's land area, so it isn't a real constraint.