One more suggestion, if you think it would be feasible:
Would love it if girls could attempt to keep wearing clothes for as long as possible.
I'm thinking a simple thigh-length skirt and a jacket or open blouse. As tits grow, they peek out of the blouse that no longer can fully hide the breasts. As asses grow, the skirt rides higher and higher until it just bunches around the waist.
Would love this even though I realize girls can pretty quickly outgrow any type of clothing.
Sometimes a girl with no job (where they currently walk around randomly) will attempt to cover her breasts or pussy. After the first time she does so when her breasts are simply too big for her arms, she stops trying.
If you add a gallery function with pictures and stats (see above) the girls that are still able to wear clothes will be featured with two pairs of photos: dressed and undressed. Nude girls not too large to cover up will do so (random chance of covering either their breasts and their crotch) to give off a "coy" or "teasing" look
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Here's a suggestion perhaps mostly geared towards weigh gain lovers (it's after all one of tags listed for this thread)...
You can trigger a prize ceremony, you know like in sporting events with a podium with a 1st place, and 2nd and 3rd runner-ups.
This would crown the three currently heaviest (largest volume?) girls, where breast and size (or volume) is added together with belly size. The size (or volume) of a girl's belly is of course much more temporary, but it could also be the deciding factor - since, as you know very well, a girl can be filled up with insane amounts of cum, which then translates to a relatively lesser degree of breast or ass growth*.
Anyway, the player presses a hotkey, and you get a "winning" screen with the three girls cheering on a podium and perhaps even a bit of screen candy (ideas: wearing a laurel, ribbon or medal, a bit of glitter raining down, a sound effect). Press any key to continue (so the player has time to do a screen shot!) Maybe have this cost a liter of cum or something, so it isn't infinitely repeatable.
*) you know better than I the exact ratio of cum to growth. I can only see that ingesting a certain volume of cum translates into maybe a quarter of size increase, but it's hard to tell more exactly...
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Just piling on... (don't feel you need to implement all my suggestions at once...

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Maybe there could be a way to make individual girls able to act on their own, automatically feeding their breast milk or ass juice to the nearest guy.
I do realize this could reduce the game into nothing, basically a "demo" where if the game does the hard work for you, all sense of accomplishment is robbed from the player. So this should be a special reward, say pay 5 liters of cum to promote a single girl to foreman.
Earlier I suggested these supervisor or otherwise "promoted" girls could, if left to wander randomly, run towards a cock that's about to erupt to sit on it (or drink from it), but here I'm more thinking about how hectic and unmanageable the game can become if you have many girls working at the same time. With enough girls and/or big enough girls, eventually you'll end up with at least one girl starting to drip (indicating her breasts or ass is full of juice) every second, and there's no time other than letting them sit or breastfeed guys.
If "special" girls could handle themselves, you would still be busy directing the other girls, but you would also have an "end game like" reason to keep collecting cum (because this could would increase exponentially just like the costs for more girls and guys) - efficient operations would basically require at least some girls doing tasks automatically, or eventually you'll see it rain ass cum and breast milk all over the screen.
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Another "maybe for later" idea:
I would love it if the guys could sit or stand by themselves.
I would love it if a guy with a raging hard-on that's getting blue balls (see suggestion above) would stand up and find a girl that's otherwise unoccupied (=randomly walking around) to fuck or facefuck. He simply can't stand the ache any longer. The girls do understand he needs release, and do their best to drain his balls of every drop.
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This would also allow my dream of a DP - where a girl that sits on one cock gets a second cock in her mouth, both guys cumming inside her at the same time. Maybe this could give extra bonus points of some sort!