Diphallism is a natural phenomenon in the world on snakes and sharks also occasionally humans so I think it would be a good option if it wouldn't be too much trouble. And the ability for 2 different types might help with creativity or creation of currently existing fursonas

I would like to have the ability of letting a tentacle makes its way through the gastrointestinal track, starting from either end, and that would be pretty cool if this game has that feature.

Inserting a characters muzzle into another's pussy/ass

If any of you have seen that one H0rs3 webm then you might want to see this in the game

okay so i thought it could be interesting if there were "real animal" mating. there could be many different animals that would need a type of breeding stand. though the point is that you cant control the animal in question more than what hole to use so to speak. once it was started it would be no turning back until the action was complete, speed and length of each animation could be random for a better individuality. this could also be a late game store item where you first would need to buy the addition of a barn to keep the animals in then be able to buy the different animals and different breeding racks. you could possibly also use the breeding racks without the animal.

A system where a mind controlled test subject will want to stay forever. Perhaps you can use their rack like furniture, placing them for public use. Maybe there could be a sleeping system to accentuate this. 

Maybe this could work with the possible material transformation fetish. A character that is turned into latex could be fashioned into actual furniture. Or possibly sex toys and clothing. A butt plug can't ask to leave after all...

https://fek.userecho.com/communities/1/topics/1021-manual-trigger-for-orgasm

It's a real pain in the ass to finally cum in an orifice or to cum at all, so either there should be an erection bar with you all the time and not just in the shower, or you can get gradually hard by pressing 'I' on the keyboard, and to orgasm, press 'O' for that.

I think the best option would be an erection bar with you at all times anywhere, an orgasm button right next to the bar, and the manual key option to orgasm with the keyboard.

In rack 1, you had only 1 milking machine, 1 fucking machine, 1 chastity cage, 1 of each kind of dildo, and it may be nice to have multiple copies of each. multiple milking machines, multiple dildos, several copies of most or all toys would be nice. that way, we could have the exact same thing being done to each subject, without leaving anyone out.

http://fek.userecho.com/forums/1-general-suggestions-and-ideas/topics/909-breastplay/

I already know that there are suggestions of breastplay, boob-fondling, and titjobs, but I think flat-chested individuals or sizable pecs should be included as well. There are people that are into the fun and intimacy of laying one's hand or handling an individual's chest, whether that'd be flat-chests, pecs, or tits (regardless of gender).