The thing i am most excited about is the six toggle-able game modes we are going to be getting. So far two have been announced. Apocalypse and secret societies, it is also confirmed four more are coming. Apocalypse seems self-explanatory. More natural disasters, extremely powerful natural disasters, and a way to control them through the soothsayer unit. Secret societies sounds super interesting! The only thoughts on the top of my head are more powerful espionage and perhaps some more tools too achieve a diplomatic victory. These will already completely change the way the game is played, and this is only two out of six. So there are already four more we have no idea about. In terms of what they could have, many 4x games now have a 'late game crisis' mechanic. A powerful AI controlled faction appearing in the late game and going all out for world conquest. I initially thought that this would never fit in with the civilization franchise, but because the game modes are taking a much looser approach too history i can see us maybe getting a rogue AI uprising or something along the lines of an alien invasion. We might also see a game mode based around plagues. But even if these are the third and the fourth that still leaves two more i have no idea about. I am very interested in hearing peoples thoughts and speculation on what they could be.