Imbalances in birth ratios have been noted in some countries, e.g. China, and some specific communities in other parts of the world, where gender selection has become an option. I think it's too early to predict the impact on the treatment of women.
Still, closer examination of the argument raises some interesting questions. For example, it seems that the government is attempting to balance out supply and demand for wives. This is flagrant interference in the free market. Plus, it's a bit weird. Also, the argument makes assumptions about how polygamy will affect the values that society will adopt in the future. Shouldn't the government respect the will of the people in this time frame? It's something to think about.