I do believe a female mannequin would be a worthwhile addition. The biggest advantage would be to stimulate selling female animations on the marketplace. Last time I checked, there is one female movement set on the marketplace, which for demonstration reasons had to include its own female model. Compare that to plenty of male models. I realize that the disparity could be in part due to animators being predominantly male (?) and most game’s protagonist being male so it being more feasible to produce male animations.
Currently, to sell female animations you have to be an animator AND modeler, or you have to have permission to include someone else’s female model. You can’t demonstrate female animations with the male mannequin, after all. I could see this is a huge barrier for animators. Additionally, having an “official” skeletal mesh would help with the quality of female animations. An animator might submit animations that look good with the included custom female mesh, but due to skinning would look bad with other meshes. If there is a standard mesh, animators have no excuse to submit animations that don’t look good with that mesh and modelers/riggers can use that mesh for reference.
I don’t think these are the OP’s points, but I think its worth considering. 