Before they do that they better stop birth, because we would have some serious problems on our hands.
If you brought the bottom ~2 billion up to the median global living standard, the total human population would begin to contract due to the reduction in new births brought on by the higher standard of living. If you reach an income level on par with poor Eastern European nations ($10k to $15k), you start to see a decline or flattening in population.
With accidental deaths, and the huge drop in new births, it wouldn't take very long - relative to the new life expectancies - to cut the population of the planet in half.
If all people stopped dying at 65, and say lived to 400, the wealth accumulation would be substantial for most of the poorest (which currently reside in China and India). Their standard of living would skyrocket, as they'd have perhaps 300 good working years. Those 1.5+ billion poor living in China and India would also likely live long enough to see the conditions of the poor in said countries improve immensely. Not to mention the remarkable breakthroughs in technology / medicine that would occur during their lifetimes, a further multiplier lifting them up out of current levels of poverty.
1. Living longer doesn't mean your standard of living will rise. Even if you work longer, you will not necessarily accumulate significantly (or perhaps even any) more wealth. And if you are in poverty currently (ie, effectively earning nothing), multiplying that by another 300 years still leaves you with zero.
2. If there is any change to the accumulation patterns of money, I would suspect that either the rich would get (individually) richer -- or perhaps more money would be printed, thus de-valuing the existing money.
3. Being at the median global living standard does not guarantee that you will produce fewer children. For example, there are many people in Western countries who for religious reasons continue to produce large families. More time for them would presumably result in even larger families.
4. In fact, Africa is particularly interesting, because its birth rate is NOT dropping as fast as predicted due to economic development: http://www.economist.com/news/leaders/21598648-birth-rates-a...
2) I'm not sure what this means. We already have an inflation-controlled money supply, and the patterns of both acquiring and printing money has changed vastly over the past century or so.
3) That article tells you straight up that those parts of Africa are missing out on the important parts of economic development that lead to lower birth rates, namely physical safety and access to family planning.