The downside, of course, is that a backlash may occur, as many boys who also have scientific aspirations will feel cheated as they watch girls given headstarts and extra aid. There are many, many school and after-school programs in science that are girls only, but not as many which are co-ed, and none which are boys-only.
Actually it should come as a relief to realize there are twice as many potential scientists and engineers on earth as was first thought.