There are social problem in the not-so-distant-future, truth be told. However, given the economy of China in the past decade or two, allowing further population growth (in an exponential manner) seems most unwise. And to say the shrinking workforce in the upcoming years? If the working force in China is all machine-aided and efficient, the shrinking workforce may not be as horrid a change as predicted...
I dont see in the near futere there will be any shrinking workforce. I guess the true problem of the one child policy created an imbalance of male/female child rate, so in the future many people will have difficult finding a marriage partner, creating social unrest.
Oh, there certainly will be social unrest, loads of idling young males and all... But the shrinking workforce may very well be a problem if the older generation continue to experience longer life-span (which kind of equates to increasing medical bill and all)...