I'm sorry but as another "Founder" there were female only outfits from the very start. The slave outfits have always been female only and have never been wearable on a male character.
And yes the developers have stated multiple times throughout the games history that the characters sex is not something they are able to change once made. There is simply too much baked into the story and how the npcs respond to characters based on their sex to enable that to be changed now without breaking large portions of the game. Not putting a system in is not an attack on the Trans community it's just an impossibility due to existing game code.