I fully support this proposal!
In theory, making a character pregnant ought to be fairly easy (from a programming perspective
). I'm not sure what software the devs have used to create their character models, but I know that many 3D development programs, such as Poser include a pregnancy parameter for all female characters. It's essentially just a variable you can adjust; 0.00 is the regular character, 1.00 is mommy on her due date, and you can set the value anywhere in between for any stage of the pregnancy you want.
Though to be honest, I suspect that pregnant bellies are unlikely to become a game feature. Mainly because the devs of this game seem to be sticklers for quality.
It'd be easy enough to create a straightforward distortion mechanic to warp the women's bellies into a complete baby bump. But when women get pregnant, their breasts always grow by about 2 cup sizes; and if the devs were gonna factor that in to the equation, they'd probably also want to redevelop the breast physics so that the new, enlarged breasts move authentically. Judging by the fact that they recently had to add a patch that exclusively corrected Lety's breast physics, I'm assuming that every single girl in the game has her own breast physics programming; so you can imagine how big a task it would be to develop pregnancy breast physics for every single female in the game!
Then there's the question of clothing. As it is, my understanding is that all the characters' clothes are tailor-made (excuse the pun) to fit their own unique character model. There have been requests in the past for story creators to be able to swap characters' clothes, and the devs have responded that this will probably never happen, as each piece of clothing needs to be specifically developed to perfectly fit whichever character it is intended for. So you can't just attach Ashley's revealing top on to Amy's body, as they both have very different body types.
Needless to say, when you have the capability to alter a character's stage of pregnancy, being able to clothe them under these constraints becomes virtually impossible. So a pregnancy belly feature would basically need to be for nude characters only. Personally, I would still love that, but as I say, I don't know whether the mods would be comfortable including such an incomplete feature.
And on top of all that, there's also the collision matrices to consider (e.g. making sure pregnant women can't swish their hands through their own bellies), and the motion mechanics, since heavily-pregnant women don't walk, they waddle.
As I say, I personally would fully support the inclusion of a very basic feature that does nothing more than expand the character's belly, to portray pregnancy. Even if it only works for nude characters, and it lacks all the polish needed to create an authentic pregnant woman. But from what I've seen, the devs of this game either do a complete job, or they don't do it at all.