This is probably planned to be implemented in the future but paw-related fetishes like being able to recieve / give pawjobs and pawworship would be a great addition tot eh game.

some juicy muzzle fucking :3

Have meters or something available which will ultimately determine the subject's fate, will they choose to leave, will they choose to be your pet, or will they choose to stay and live there?

Similar to tentacles, urethral sounding, cbt, and oviposition, often but not limited to, a penis. The tentacles or whatever jam in through the urethra and you can see them distend through the urethral canal all the way through in to the ballsack as they play/squeeze/eat the testis.
This fetish often interplays with internal views of anatomy and whatnot, everything from cross-sections inside the penis, to x-ray views inside the ballsack.
Could be fun considering it's also a cross-section of a lot of fetishes.
This fetish also uses maggots or insects, which I am not a fan.

The idea is based on the machine in this cartoon: http://www.youtube.com/watch?v=isbzfRh4za8&t=4m11s

It works the exact same way, except it pumps out a guy's cum by
non-painfully (or painfully if you prefer) pounding on his underwear
bulge. The milkee's balls/bulge are grown/inflated via a serum, which
also works as an anesthetic to negate pain, allowing the milkee to feel
only pleasure from stimulation to the balls bulge. He's then strapped
down tightly to a table and gagged via whatever gag the milker prefers.
The pounding apparatus then pumps out the milkee's cum through forced
orgasms, deflating his balls/bulge back to its original size as it
drains him(it can even pump his cum out through the fabric of his undies
if desired). The milker can do as he wishes to the milkee while he's
being milked, such as teabagging him, face-sitting, talk dirty to him,
lick him, tickle him, play with his nipples, and so on and so forth. It
can be consensual, or non-con, you probably get the jist of it.

I mean like in Fenoxo's TITS. Being able to make a subject/pc lactate chocolate milk, honey, and stuff like that. Substances which aren't normally produced in breasts. And being able to fine tune how sweet, or thick it is.

I think fek needs to implement a system where you can research a latex substance that can transform a host into a living sex drone slave that you can order around, break, toy with, use, own and sold.

Would be a very interesting game mechanic plus not alot of porn games do this

Reference:

Basically a set of machines that the player can strap themselves or others into to run an automated experiment.

Being deepthroated by a long tongue is one of my favorite fetishes. 

Ungulatr is the best artist for this fetish.