It is obviously not going to magically happen with the snap of a finger, but if transgenders want to compete fairly, they need to compete in their own leagues. Men who transition will always have an advantage. Even if all muscular and cardiovascular benefits are guaranteed to be negated, which they aren't, men have totally different skeletons: longer arms and legs, smaller hips, wider shoulders, wide cheekbones, a larger jaw and brow ridge. As is, transgender athletes are hurting the integrity of sports.
Taking steroids even once is shown to have permanent effects on muscles' potential. Men have upwards of ten times the testosterone of women and effectively are on anabolic steroids, relatively speaking.