India won't be a super-power. It has too many regional challengers. United States was lucky it is surrounded by oceans and two friendly nations in the north and south and thus was able to project power and not enter into a regional arms race with either Canada or Mexico.
India has to contend with Pakistan, China, and other countries and thus cannot achieve breakout potential to dominate the world the way USA does.
China too has the same problem. It has too many regional rivals. Japan, South Korea, Taiwan, Vietnam, Australia, Indonesia, Malaysia, Singapore, Philippines, India, Russia, USA.
On the whole, the era of super-powers is coming to an end. Once China surpasses USA in GDP, the world will be a multi-polar world rather than singular polar that it is today.
So China or India, won't replace USA as super-power but rather it will be a leveling off effect. A similar situation in Europe before World War I where Germany, England, France, Russia, Japan, Italy, USA were more or less equally strong.
For the 21st century it will be USA, China, India, European Union, Russia, and Brazil but US will continue to be the leading global power for at least another 40 years.
