Most countries birth rate falls off as they become more developed. There’s estimates that the world population will stabilise around 11 billion. I don’t think there’s any theoretical reason why high quality affordable high density housing is impossible.
A condo/apartment future is actually pretty likely, and achievable. NYC and most of the non-US world went that way in the 50s, and a lot of Silicon Valley cities (which were previously all suburban sprawl) have been constructing those 4-over-1 condos like crazy over the last 10 years. Even notoriously anti-development SF Peninsula cities have gotten in on it.
But that's largely not where the real estate feeding frenzy is - condo prices are up, but nowhere near as much as SFHs. Turns out a large proportion of Millennials still want a detached house with a yard in a good school district, the same thing that the past several generations wanted, but that dream is increasingly unrealistic.