The idea of having a sidequest sort of thing where you go about doing a long term series of experiments and sciency sexy time with the end goal of breaking a person's will (for a variety of reasons) or altering their mindset into accepting a new fetish or sensation they otherwise wouldn't enjoy, or make them orgasm from sensations outside sexual stimulus.

an example scenario for what I mean in terms of changing mindset / breaking willpower is:

Have a straight, male subject come in and then strap them into a long term holding cell. Your objective is to break them into enjoying anal, despite how fervently they're against the idea. You set them up with something to stimulate them anally and a device to pleasure their penis so as to gradually get their mind to attribute anal stimulation with regular pleasure. You set them up and they're held there like that for a set period of time (can be adjusted for gameplay convenience) and you check in on them every so often to see how they're doing, see how many times they've achieved orgasm, willpower, sensitivity, etc. You can also take the time to speak with them, offer some opportunities for humiliation or encouragement, depending on how sadistic you want to be.

Depending on their progress, you can add or modify the current devices offering the stimulation. For instance, you can enhance the anal stimulation to produce a more pleasurable sensation but keep the penile stimulation at the same level. OR, you can gradually reduce the penile stimulation.

After several sessions of this, eventually you'll set it up that all he has for pleasure is anal stimulus, but he's far enough along that he might just climax from anal alone.

Once he's achieved several orgasms from just anal stimulation, you can set him up in the main experiment area and have some additional fun with your subject and see just how much they enjoy anal now.

Depending on whether you humiliated them or encouraged them, they might take to the sensation of being brought to orgasm anally and it'd be less of a "mindbreak" and more of a "Mind opening" for them (happy end) and they enjoy anal now.

OR, if you were more sadistic and constantly antagonised and humiliated them during the process, they become resentful and hate the notion of being able to climax from anal stimulus, opening even more opportunity to antagonise and humiliate the poor guy. ALl the while they detest being given anal stimulus, even though their body craves more of it. They can either eventually break and give in to their new desires, or remain steadfast in their rejection despite how desperately they need their ass to be plowed.

Another option is tricking their mind into believing that they can't cum without anal stimulation, watching them try to masturbate and be unable to cum without having something in their rump, or being unable to cum unless all they had was anal stimulation.

An example scenario for climaxing from sensations outside sexual stimulus:

Have either gender individual in a similar predicament, only this time, your objective is to get them to cum through other stimulus not typically associated with sex. For instance, tickling (or tickling specific parts of the body)

for example, tickling the navel of a female while having her lady bits recieve proper stimulation so that eventually her mind attributes tickling with sexual stimulus until she can be brought to climax by tickling her navel alone.

Another example of this is fondling of the ears or other such sensual touching that doesn't involve direct sexual stimulation. Same rules as above, offer the sensation and give sexual stimulus until the subject associates the sensation with sex, then repeat until subject can orgasm by just that sensation alone.

TL;DR: give the ability to have a side quest (possibly with its own test chamber) to modify the behavior of a subject through mental conditioning to whatever the player desires, specifically: implanting them with a particular fetish or having their body react with sexual arousal (to the point of climax) from certain stimulus that isn't supposed to be sexual, or is otherwise not something that would arouse the subject to that extent (such as a straight male receiving anal). Also make it possible to do the short and fun way in the main lab for those short on time or who prefer a more hands on methodology.

I hope I explained this in a way that folks can understand.

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-/

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

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

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