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.

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.

Ennjoying ejaculating quickly or watching another person do so

Perhaps it would be possible to have a rope bondage feature where the subject could be tied from a suspension post in the ceiling?

As bad as it sounds, its a really common fetish on the fandom, adding an option for having forced sex with a subject, or change their tastes like on rack 1, so they dont like what its being done to them should be a thing in the game

Not only giving the subject the ability to be a dominant force on you but also having a revenge option which will allow the subject to pay you back for everything you did to them (with or without their consent)

Not to the level of C&BT; just the ability to set a sheath swaying or balls swinging.

Maybe be able to put clothes on characters on the rack, Have a character in his underwear or even wearing full pants and then interact with him, jerk him off through his pants or hold a vibrating wand to his penis and cause him to to cum in his pants. You could have it as a separate fetish/preference slider, where some characters might not mind to much or be aroused by it, but some characters would absolutely not want to cum in their pants; it could make them embarrassed or feel humiliated and try not to cum until you take them off. You could expand on the speech system too where if they are getting close they beg you to take them off quickly before they make a mess. or if they are leaking precum they comment on how they are making a mess ect. Or when you tell a character to cum they can comment how they don't want to until you take their clothes off and try to resist. and when they do cum or are leaking precum, you can see visible wet patches wet for precum and dripping white like on the characters bodies for actual cum