For the Cervix penetration, I think it'll need an X-ray window to better display this kink. It is feasible, but it'll not be easy; this will also require me to add effects like internal cum shot and such, and the movement of penetration needs to be synchronized. Another way is the NPC will tell the player how she feels her cervix ram during sex.
About Futa, I will have to consider whether adding the content will be worth the additional development time. As for the technical aspect, both male and female models can be equipped with each gender's genitals as I originally designed them. I may start a poll for this topic when the time comes.
If I could suggest something that would make it work even without x-ray, it is to create a certain step and not make it immediately possible, unless forced by use of substantial force and speed of the insertion, implement pain thresholds and different moods/state of mind that occur upon immediate forced insertion for it (and other things, depending on characters fetishes and preference, they might hate it/be in pain or receive immediate orgasm or just have a mind break and become a lifeless onahole)
Generally you want to have certain amount of resistance for penetration, especially with cocks that become thicker (sheath on horses cock, knot on canine cock, example: for horse cock, intially lots of resistance as the head goes in, then it goes down but still high, as time passes during intercourse character loosens up, but there is still gonna be another step when sheath (or whatever that thicker part further down the shaft is called) goes in, then it goes up once again and resistance stays higher for a long time, every time cock is pulled out and the sheath comes out, there is a pop and once again a pop when it goes in, when character is super loose and whole cock goes in effortlesly (but still not all, for cervix penetration there should always be some cock "available" to go in for obvious reasons but also to make it visually appealing, we assume character becomes also deeper as they stretch, but for foced entry we can go all in from the start and burry whole cock in one swing if one wants to, but if we want to go slowly and not cause character to be in pain, we allow it all to stretch, lubriacate, at this point the depth is significant, but we always want things to work in such a way there is some cock left to go in) then we can go through cervix in "pleasureable way" and when it goes in, we get a massive pop and resistance doesn't go up but every time we pop in and out, there is a lot of it temporarily, we never fully drop resistance of the cervix to zero, it should be always there) but also just for very thick and long cocks, of course bulge would have to go along with it, whereas smaller cock might not make any, longer one will but it's gonna be less pronounced/thinner, full on fat bulge with thick cocks and generally huge one with cocks both long and thick, as it hits the cervix it's where there is most resistance, a very thick one might not pass through it unless character is into pain and wants you to push it super hard or is super wet/horny and it slips in eventually thanks to excessive lubriaction/wetness, as cock pushes against the cervix, the bulge becomes larger towards the top, pushing outwards (away from body, almost as if trying to poke through belly), but once it goes in, the bulge actually goes down but occurs much higher up the body and from there it's possible to go ridiculously deep inside (the stretch is actually easier once inside, we assume hentai logic that once past cervix - no limits, or at least to the usual "crazy" level abdominal bulge where cock starts to cause bulge almost between tits (hentai logic of course, let's not worry about internal orgasm, we know characters in sex games are just big onaholes)
If you end up implementing it all, you will literally make the best sex sim there is, godspeed you by perverted furry friend.
And don't forget cum inflation, if you do I'll find you and pull of Liam Neeson on your ass.
