Nice concept! I really would love to see on top of breast, butt and hourglass a overfilling form where you can overinflate them into full blimos too maybe with a settings switch where you can choose from a more weight gain scenario for blobs or a inflation based one for blimps? Hopefully you could also create some interesting game over screens for those who overfeed/fill there cow girls. Like example for blimp it's a cartionish popping with milk splattering the screen in a game over. Or for weight gain it's a splash of gravy and corn or something that replaces the milk game over logo. The goal basically being to make your cows thick but not go overboard and indulge them too much maybe with different cows having personalities? Like one loves to eat or drink so you have to not indulge her fantasy too much to win or shell pop
Another girl could be nervous and not have that stretchy of a stomach so you're goal could be to fill her up as little as possible as she expands from the littlest of food/drink making it pressure sensitive as you have to carefully tap the feed button as holding it or treating it like normal cows otherwise her face will widen with fear and she'll rapidly inflate and pop
So basically each cow could have there own quirks that could leak to a pop if you don't watch out for them?
You could give interesting names designs and backstories to each one as well if you like. Giving the audience incentive to care for them and not to pop them.
Either way this seems like a fun concept I hope you go far with it and make it as interesting as you can!