Agreed jings and bookdreamer about it being a retrograde step if it were to happen. Let's hope it doesn't.
The underlying problem, and why this suggestion has been made, is that some men are still thugs when it comes to women (some women are thugs too, let's not forget). The issue at large is how society deals with, or rather prevents, assaults from happening. If there is a rising number of late night attacks on women on trains by men then those trains need more policing, more police patrols at stations and even perhaps on trains.
I honestly don't see how carriages called women only carriages would act as a preventive measure.