Thought about somthing similar (not directly related to trans characters).
For Male player characters: The option, in bedroom scenes, to choose between having standard intercourse or using your hands. Since the lesbian scenes are already there (which i naturally enjoy btw) this should not make for too much (re)writing.
And vice versa the option for Female player characters: to use a strapon and play the male type interactions.
Both would offer a cool variation for storytelling, and ofc you could also extend this by differentiating the outcome, some characters enjoying one interaction more then the other, maybe challanges when getting fatter ... u get the idea.
regards,