I. e. a knotted cock will get stuck in a hole when sufficiently excited and inserted deep enough.

Staying there unless forcefully removed with a sharp tug, expelled by a very unhappy partner, or the excitement level falls low enough that the knotted cock can freely slip out.

A tied knot should give (extra?) stimulation when tugged outward (but not free), and possibly act as a hindrance (but not completely, if implemented) to cum spray.

Basically just making the subjects' belly bulge after they've been filled enough, and maybe make the cum start coming out of the other end if they're full and are still being filled.

You know that portrait system for when characters talk? Let's use that and make it so that it can display X-Ray views during sex as well.

To be technical, this would not just by the current camera that is just zoomed in too close. It would be showing a "copy" of the player character's/power bottom's penis, one that doesn't contort or warp to prevent clipping issues while it's being smothered by the retriever's insides.

For said insides, I'm thinking we'll have to be creative. A combination and 2d dynamic pulsating overlays along with 3D models that have internal detailed textures but completely invisible external textures, to allow for free moving camera that's not stuck to just one angle.

And of course, this could be used to show the cream pie flooding of vaginas, mouths, wombs, throats, intestines, etc, etc.

The males have a great variety when it comes to dicks, but the girls with pussies? Not so much. I'd just like to see the option for canine pussies right next to canine dicks, equine pussies next to horsecock, etc.

Penetrate test subject with Penis and Dildo, multiple dildos or Penises (Portals?)

Double anal / vaginal or anal+vaginal

Love the cock milking but would also love to see some breast milking as well!

Penetrate the Sheath or Slit of a male with a Penis or Dildo.

Was thinking of something maybe along the lines of an NPC you could custom create as sort of a lab partner. Maybe to use as a subject to test certain fetishes on, fool around with, ect. Could even be part of future fetish implementations for exhibitionism and such where they can also observe and assist in testing.

The ability to inhibit orgasm through various devices, chastity cage, chastity ball, chastity belt, or even an orgasm inhibiting headband that prevents the pleasure center of the brain from sending the climax signal, to really build up that need.