The discussion so far is proof that there are still lots of features that can be added for this expansion; hopefully they'll put a good amount of work into it. The release of this expansion should also mark the imminent release of the .dlls for modding, and pitboss, hopefully. (The .dlls should also allow modders to add tobacco if the E rating doesn't allow it).
Because negative effects from resources you acquire by settling a city near them and improve them sounds like a very bad idea for gameplay.
If anything, it should become "obsolete" (not negative), and at the same time that other Luxes appear on the map to make up for the obsolete ones.
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War weariness could be implemented given the "One World" concept. I could definitely see it becoming a bigger factor in the late game, while still giving some players a reason to use the late-game units. But they have to be careful so it's fun and not frustrating. As an example of implementation:
if you declare war, you start with an empty "war weariness" bar.
- Over turns, the bar fills itself.
- Losing units fills the bar, and damage to units slightly fills it as well.
- Destroying enemy units helps empty the bar.
- Damage to cities helps empty the bar, but when the city gets the health back, that effect is reversed, so the city must take more damage than it's healing for it to be of use.
- Conquering a city empties a lot of the bar.
- Making peace removes the bar from play.
- Offering peace with no conditions empties the bar.
If the bar is overfilled, temporary unhappiness is added; more overfill means more unhappiness. As the overfill is removed (or peace is made), the temporary unhappiness goes away too.
The reason for all this detail is because I don't want to give the wrong idea of what kind of war weariness I'd like to see in the game. War weariness sounds like a logical step fitting with the name of the XP (as well as being a feature in earlier games), so hopefully they'll find a good way to implement it.