MAG and WAG are just so different. Men's and women's basketball, or ice hockey, or curling, or whatever, same sport, same apparatus, same rules, etc. Maybe softball/baseball have differences, I don't know much about that, but can't women still play hardball and men softball?
I feel that if you have a girl who is more into power than grace, excited by rings or parallel bars or whichever, and is able to brave the stares at competitions, she should be able to do MAG, no problem. And if you have a boy who is graceful and flexible and loves the movement in WAG, and again able to brave stares, he should be welcome to try WAG. This will be a very small percentage of the gymnastics population due to nature and nurture, etc. but it should be an available option.