Why should it matter if there are fewer female engineers than male engineers? Women outnumber men by a large percentage in most humanities graduate programs but it would be absurd to suggest we need to do something to fix that situation. People have gotten so caught up in the numbers that they have forgotten the *REASON* we care about underrepresentation.
THE REASON TO WORRY ABOUT THE UNDERREPRESENTATION OF WOMEN IS BECAUSE YOU BELIEVE WOMEN ARE BEING DENIED A FAIR OPPORTUNITY TO PURSUE CAREERS THEY WANT.
This supposed solution is at odds with that concern. After all, if women aren't entering engineering simply because they don't find engineering jobs as attractive (and not because they were discouraged) there is no problem at all. Both men and women are simply choosing the type of work they prefer to do. If it turns out that women find work that is more socially meaningful more fulfilling that's great for them and we shouldn't mourn because they choose the type of work they prefer.
Moreover, this kind of "solution" doesn't really address the underlying problem we care about. If women are being discriminated against or discouraged from studying STEM subjects then no incentives at the college level removes that discouragement or discrimination. Even if you gain gender equality in engineering you haven't made things any better if, but for discrimination/discouragement, women would have made up 75% of the profession. This is just a band-aid to make people look better not a solution.