For obvious reasons, everyone talks about a world dominated by China. China is likely to have an economy which will be x times larger than the US on the future's horizon. For the moment, assume the economic size is remains tied to the population size. Which case, the projections I have seen for India's population in 2050 is larger than China's by a fair bit. if the world stabilizes around then, population wise, circa 2100 its probable India will have a larger economy than China will, even if they have the same per capita economy. Even more so, should China be unsuccessful in reversing the one child policy, say, because the family size has become cultural, this could be even worse (though to be fair, India's TFR has fallen considerably, too. It does remain above replacement).
Projecting 2100 with rigor is hard. However, that's never stopped science fiction! On the other hand, let's try to keep a little rigor here. What WOULD an Indian dominated world look like?