For all the historical significance of China's decision to abandon its one-child policy, the move risks falling well short of reversing a trend that threatens to throttle economic growth.

It's "too little, too late," said Shanghai-based Andy Xie, a former Morgan Stanley chief Asia economist, about the Communist Party's approval of plans to allow all couples to have two children. "The population will begin to decline in 10 years. Why keep population planning?"

The official Xinhua New Agency reported the new policy Thursday at the end of a four-day party gathering in Beijing. The relaxation is part of President Xi Jinping's five-year blueprint for transition to a "moderately prosperous society." As the days of cheap and abundant labor fade, old growth drivers such as manufacturing and construction are stalling. While China's aging population may boost consumption's contribution to the economy, the challenge is ensuring economic dynamism doesn't fade as the share of young people shrinks, as it has in Japan.