Well, I don't need anything Xrated, the pillow talk we get from companions is good enough in that regard. I wouldn't mind them adding a hug, or maybe a kiss animation if it was done well. But then, we'd have to consider peoples sensibilities, what's a dignified kiss that would be "okay" for both genders, and sixualities. Anything considered "passionate kissing" can easily become awkward to look at if its not done well.
I *do* admit, the fade to black in FO:NV with black widow benny, was hilarious. However.. I wouldn't really want to hear something like that every time my character sleeps next to/with their lover.
As far as transgender goes... theres a certain NPC already in game who is close enough to representing something like that for me, anything more should just be left to peoples personal interpretations of the game, and their own character's role play.