Making a gay or straight test subject have sex with the gender they do not like. could be done with portals, or just machines, or persons.

I'd like to see the ability to go sword to sword with a subject and use a single fleshlight/masturbator sleeve on both. Trying to time both the player and subject cumming in the same fleshlight at the same time could be a fun objective.

This is similar to http://fek.userecho.com/topics/242-internal-or-x-ray-viewer/, but I have a feeling it may be easier to do than having all organs in 3D:

On inserting an object into any orifice allow a 2D cross section view to be displayed of the object moving inside. This would be especially interesting for delicate procedures like sounding, urethra play, vaginoscopy / uroscopy. It would combine great with http://fek.userecho.com/topics/401-/

After the first sex session, the characters libido and sex organs (breasts, penis and balls) increase in size. 

All right here me out on this one. This would be a very late game item that would allow you to put subjects in to "travel time" (whether its just a mind perspective thing or the real deal is up to fek). For example if you want to have an extreme edging session you put the subject in the machine set how many minutes, hours, days, or even weeks you want them to "experience." 5-8 minutes later you come back to the machine and find a subject that would be very exhausted from edging.

I think this would allow some fun interactions with the dialogue system and to even use it as a punishment tool

You should add the option for an enema in vagina or ass then be able to plug it.

What it says on the tin. Just be able to aim a showerhead at the nethers of a subject for some messy / squirmy fun.

The ability to insert penis/finger into nipple.

Cumming while inserted causes breast to inflate.

Super simple.

Alternatively a toy could be added to milk cum from a subject, then inject it into another's breast/ass/vagina, and inflate that way.

some gagging visuals that can be shown with the eyes/body surging, maybe some sound effects or text.

Throat bulging if the dick is big enough 

Just like the header says, making every single clothes piece be available no matter what the gender.