Not sure if this has already been suggested.

If a test subject has a huge cock, it'd be hot to be able to fuck it. Put your dick in their urethra and fuck it.

Not only that, but if their cock is smaller than yours, you can envelop their cock with yours, kinda like a fleshlight.

Since it looks like Rack is getting an update to fluid physics, why not add more fluids to the game?

The hymen is a membrane found at the outer opening of the vagina, and is typically torn by careless lovers, emitting mild amounts of blood.

Would love to see female subjects getting really wet to the point of dripping when extremely aroused.

The selection of different penis shapes is diverse enough for R2CK's current state, but I feel like the female side could do with some variety too. Different vagina shapes such as a canine/equine look would be relatively easier, scalies would be fine with the current slit option. Perhaps an option to decide where breasts can be too? (Multiple nipples, different placement like the inguinal region for some hoofed animals)

Going forward, some more variety in penis shapes would be good as the species list expands. Not every species with a 'knot' looks like a dog's. Alternatively, a slider to control the smoothness of features like the knot and penis taper?

Because 2 aren't enough sometimes. An I'm not just talking 4 or 6, we should be able to add as many breasts to our avatars body as we deem necessary.

Or until our framerates start to dip, which ever comes first.

Like being able to go out and do something with at least one subject, or your lab assistant. Depending on the circumstances it could be a nice date, or a big embarrassment for your companion. Maybe they don't wear any underwear, or they have something like a vibrator (that you control) on them. Or both. Or maybe having them act like a pet. Wearing a collar with a leash, eating on the floor of the restaurant out of a to-go box. Stuff llike that.

Pretty self explanatory...

A Species that is androids or robots, with body part options which there could basically be three types of; Cheap, Middle Class, and High End. Cheap parts would look like clunky parts with too much metal and exposed internals. Middle class maybe looks like less metals, smoother surfaces and plastics, hair in places, etc. High End would be space age materials, Carbon fiber/hexagon textures, shiny parts, Artificial skin and hair in some places, and high tech bits.

The body type would just be one for "Android" with differences for the body type ranges for the part quality. Other body parts, like Tails, Feet, Heads, would be Android versions of the other species parts. Even the heads, for whatever species the android was to be mimicking, or a few unique ones for just the classic "robot" look.

The Genitals Could be any number of things from being the same as other species with alternate textures (i.e. made to look like fancy materials instead of natural flesh), or perhaps even comical such as a giant Screw, or an overly simplified smooth rod.

These Artificial/Robotic body parts would also give the option for having Cyborgs, or just Characters with Artificial Limbs for one reason or another, and giving the game a bit more variety.

For those who enjoy the more "futuristic" or "space faring" settings, or just want to put something creative in.

Just optional/bonus/alternative rack/table where you can have the characters all fours, more laying position facing the floor etc. Allowing better view of the rear and penetration