From the article:

Statistician Hans Rosling has calculated that all of these scenarios are probable. I agree. If current economic development trends continue we should expect the average person's income in India and China (for example) to reach the same levels of the U.K., U.S.A., and Japan by 2048. Check out Rosling's TED talk on this: Asia's rise – how and when.

Hans Rosling's video are massively influential to me. I feel like he has a fantastic grasp on the future of human demography.

In terms of the development of Afghanistan, Sudan, and DRC, those countries represent the biggest challenges. Certainly by 2050 they will not be at the development level of China, India, Brazil, Russia, Nigeria, Ghana, and Turkey. However, they will be much improved. There are several technologies on the horizon that will help the entire world essentially erase infant mortality and many easily curable communicable diseases that still plague the developing world. And as those countries urbanize with the rest of the world, widespread female education should become more and more common.