Picture if you will the female version of the TYR Sayonara Shortjohn Swimskin above with no zipper and a textile fabric and there you have it: A de facto shortjohn speedsuit for woman.
Surface covered: Men swimsuit shall not extend above the navel nor below the knee and for women shall not cover the neck or extend past the shoulders nor shall extend below the knee.
Variety of materials: Different materials may be used in one swimsuit provided they are textile fabrics as defined above and they comply with all other criteria including notably thickness and permeability (measures to apply to total layers). Combination of materials shall further not create outstanding shape(s) or structure(s). Layered materials must be completely attached/bound/stuck together except where required to protect sensitive parts ("privacy layers").
Construction: No zippers or other fastening system is allowed. Seams shall be limited to functional systems and shall not create outside shapes.
For womens' suits I foresee swimsuit companies choosing a fabric for the core area that is more constrictive than the breast& shoulder area and then choosing another fabric all together for the back area to aid in buoyancy and compression.
Then picture a small entry opening which the female slides into thus giving them an ad hoc shortjohn without a zipper. Voilà - Woman get to wear a speedsuit!
Boys, on the other hand will lose more speed than the woman and there will be no modesty avenues to explore whatsoever. It's briefs and Jammers; just the way Schubert, Bowman and Speedo probably wanted it.