Realistic corporations is something that needs to be looked into as it is insanely annoying and frustrating to play with. The algorithm that determines if a corporation spreads or leaves a city is really messed up. At one point in my game, corporations would pop up in a city and then without fail, leave it the next turn before I could even build the corresponding corporation building. And this happened every single turn for a long time until I got into the mid-late transhuman era where they may stay for 2-3 turns but never longer than that. I don't know about you, but this is far from realistic. I feel that once corporations enter a city, it shouldn't be able to leave it except under extreme circumstances like that city going into negative gold gain.