i have interesting idea for idle games in general. How about change the expotential growth for function wich slows eg.: f(x)=x^0.66 or root of x, or maybe go a step further and use hump in f(x)=2*x^0.66-x^0.75. There will be limit where profit will not grow or even drop with next factory (or lemonade stand).
This game have so many customizing options. I think that definitely deserve second hard badge. Dificulty 140% setup, and maybe 1500 kills, or earn 100 000 000? What do you think?