In which case I can see why you'd be worried. He's basically caught in some bureaucratic limbo.

When you say that you've been told you should wait until your child reaches adulthood, How far up the food chain have you gone to be told this? I guess you've been dealing with the authorities in your wife's hukou area. If this is smaller town or city then have you tried taking it to the provincial capital or further still to Beijing. Certainly the British embassy claims that the Beijing authorities can carry out the process of relinquishing Chinese citizenship regardless of your wife's hukou area. When me and my wife registered our marriage we had to do so outside her hukou area because the local authorities there were unable to deal with a mixed nationality marriage. Is it possible that you're being told "no" is more like "I don't know" by a few officials who don't have experience of dealing with such a situation and are just trying to save time and face?