It's technically possible now, but I'm not planning on adding any hardcore Guy-Girl scenes to the main game any time soon, and probably not ever. Maybe some lighter stuff like lap dances or spanking? Maybe. Come to think of it, there are 3 male avatars so that's either triple the renders or 1/3 of the coverage, so, probably not even those. Also John is based on the older Michael 7, he looks fine from behind at a distance, but he might look a bit dated up close.
That being said, if you want to go for it in your own sets, that's up to you. All the pieces are there. John is included in the render toolkit.