The population growth decelerates significantly when living standards improve, it has happened everywhere. These sorts of estimations on future are way too simplistic, there will be disasters (by human and non-human factors) which change the growth rates dramatically. I'm quite certain India will have a huge water crisis before 2030, it will impact the agriculture there greatly. The neighboring countries will supply water to India but it won't be cost efficient (with a pipeline cost) to use it in agriculture.
It's easy to grow from nothing. Plenty of African nations have grown 6-7% per annum, I still don't believe they will achieve the level of Norway by 2100. As the population gets more complacent and used to the comforts, the growth rate will fall to 2-4%. Oh yeah, are these the same economists who forecast that real estate prices will increase indefinitely?
India may disintegrate like USSR well before 2050. http://en.wikipedia.org/wiki/List_of_active_separatist_movements_in_Asia#India British gave autonomy to Muslims/Christians/Anglo-Indians/Sikhs/SC/ST communities in 4th August 1932 Round Table Conference. http://goo.gl/wTzIq