One of the yoga places have only men and women yoga. The local commercial gyms have classes that target men and women separately. There are lots of women only clubs in town, the self defense shooting gun club for women is very popular. There are several successful all women martial arts classes and self defense programs too doing well.
I am honestly shocked at this idea. As for the women's only clubs, I have seen the so called self defense courses offered at our local Y, and I personally find them to be a horrible idea all around. Most of what I see is a couple hours a week for a month and a lot of women with a very high level of unfounded confidence that will quickly crumble if they ever actually need to fight their way out of a situation. And while I'm not sure what martial arts schools have martial arts for women only, I'd be very curious to see that lineage.
Aikido, in my understanding, is a long term study of self improvement, physically, martially, and spiritually. All of these are linked, and I can not be a good Aikidoka and work only on physical self improvement without also martial and spiritual self improvement. Martially, if the only people I am practiced at defending against are women, how on earth am I going to learn how to adapt a technique to that 6"5" 300 lb rapist who actually means to hurt me? Spiritually, we are all the same. If I deliberately exclude contact with half the human race, spiritual self improvement turns into self delusion. And as far as physically goes, no, I'm not in competition with any of the men I train with, but if my only goal is to get buff, I'm better off running laps and lifting weights solo anyway.
As far as the female comfort zone goes, personally I think women should spend more time around the men in my organization at least. Knowing that there are decent men out in the world who are kind and would do anything if you need assistance is just as important as knowing how to break the wrist of the scumbag who just pulled a knife on you.
Just my .02.