Hyper breasts or penis depending on how good you can get the image generation... Maybe some regarding body types or even impacting the bodies of the npcs if that's ever planned. Could be fun to change them around too.
Hear me out, the max pp size should go higher than 9 inches... for size queens and the like. I just say this because poppy compares it to a footlong and it doesn't quite size up to it... XXL size shock could be pretty good, especially with the grower side of things.