If there were equal number of male and female toilets. My issue is, in general, women tend to take longer in the toilet. A male only toilet line would clear faster. In how many pubs and clubs do you see women in the men's toilet because the queue for the women's is too long.
Seating-wise, why not go one step further - segregate all passengers totally by sex - put solo male passengers in the front and solo female passengers in the back with families in the middle. Society has definitely move on from this kind of view, thank goodness. I would not want to fly BA if this was proposed. Would the op want the women's are totally partitioned off? I am appalled that this idea was even mentioned.
If this was Saudi Arabian airlines maybe. On British Airways - never.