Even in Sub-Saharian Africa the rates are lowering constantly. One fact which seems to be contributing to that is urbanization. Some African cities like Addis Ababa already have fertility rates at around of 2 children per woman (Addis in fact has 1.9). This process is currenlty advancing very fast and has dramatically changed the lifestyle of people there.

Also growth rates in Sub-Saharan Africa are now lowering, in fact, their peak was in the mid-1980s, with a second (lower) peak in the early 2010s after the HIV catastrophe. In the coming years population growth will be linear even in this region.

So what does this mean for Bitcoin? Population growth can be still a fact contributing to demand until some year between 2050 and 2100 (the world's population peak is expected currently in these years), so most of us in our lifetimes, could see a population-driven Bitcoin demand until we die. But in the long term this could change, as in the whole world population could begin to decline.

However, economic growth is much more important for Bitcoin demand. And what Malthus didn't take into account is the almost infinite potential of resources in the service sector. At least in the following 1000 years that growth could last - if we don't end this tendency by our own stupidity.