keeping it at ~500 millions is necessary. Two kids per couple could work in maintaining a sustainable work force. To raise productivity and living standard by reducing server internal competition may increase quality of life for people in China. Do not be confused by some so-called experts that China could face a big problem in the near future because of shortage of young labors and of aging society. In my opinion, there is tons of advantage because of less population within China that could ease severe challenge facing people China - limitation of land, natural resources including fresh water, over expansion of cities - that obviously affect quality of living conditions.
A quick solution to shortage of labors is simply to postpone the age of retirement from 60 to 65 or even to 69.