The game quite literally cannot support an open world. Games are not magic- you do not simply wake up and go "I think I'll convert the game to open world today". There are hundreds of reasons this is never going to happen. The game is not designed to let it happen. There are so, so, so, so many aspects of everything that would need to be completely uprooted for it to happen.
200 sims is also insanity. Most players have such outdated hardware they struggle with the existing limit of 20. 200 is ridiculous and would slow down even the strongest hardware.