I would like to offer a new interpretation about that Firaxis tweet.
In the next expansion there will be a new mechanic: wonders can take damage.
The tweet was not about the inclusion or not of notre dame in the expansion. It's already in the expansion. It was about whether to include the fire of Notre Dame in the trailer. Instead, it will feature the destruction of Alexandria and others
Edit: Therefore we might also get Earthquakes, Fires and Tsunamis as an extension of GS mechanics. Fires might be set-able by great generals or maybe military engineers
and you can steal treasures from opponent's great wonders with Great Generals, including tech boosts and works of art. That was a dumb suggestion. It will evidently be done by archaeologists.
This would fit into a colonial / anti-colonial theme, so that great works will have a
culture attached to it and you'll get bonuses to culture and tourism from owning works from different cultures, which might be acquired peacefully or taken through war, with some kind of balancing feature to make it double-edged. Increased tension with the original Civ's culture at least, especially after the modern era.
If we get a multi-cultural/isolationist mechanic along with cultures and nationalism, I expect Italy and Colombia to be in the game. We'll also get Leaders with bonuses to multiculturalism while others might benefit from isolationism. Which would make Bismarck a very likely alt leader for Germany.
If colonialism is a thing, disease will also be a thing. Perhaps along trade routes, or across different continents.
And if colonialism is a thing, trade might get some changes. Or perhaps just the ones mentioned above.
It would also hint at migrations caused by both natural disasters and war.
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So, on a scale of 1 to 10, how crazy speculative is that
I need to justify my expected Civs choices.