I have a suggestion for a new feature: region (territory-based) buffs/debuffs
Given that recent updates have allowed for the diversification of nation economies (with the possibility for optional, uniquely attributed financial bonuses), I thought it may be interesting to have certain custom, completely optional territorial bonuses representative of the existence of certain valuable natural resources/territorial droughts (appropriately relevant to a player's particular scenario). These buffs/debuffs could be just be inflicted at the player's discretion during the runtime of a particular simulation (with a customizable duration and effect for the nation currently occupying the area, perhaps depending on the proportionality between said nation's entire area and the area of the affected region). The effect could be simply a numerically customizable economic bonus or even a customizable defensibility bonus of the affected land tiles.
Apart from just affecting a region temporarily with a fun economic bonus for an arbitrary reason, I feel this functionality's implementation within/for scenarios could make them especially unique (resulting in specific areas being more beneficial than others, even though the map itself is the same). The best way I think this could be done is by defining certain "phases" or "seasons" that each possess, in accordance with the player's specifications, multiple different regions with specific bonuses (edited via the scenario creator) that, after a certain amount of time has passed, advance onto another player-defined phase/season of new affected regions. There could be as many defined phases/seasons as the player wishes for a particular scenario, but after every player-defined phase/season has run in the simulation, they would just repeat (resulting in unique, customizable, and most importantly, completely optional environmental effects).
For example, maybe (for no reason at all), I wanted to develop a scenario for the world map which defined three phases in which the eastern hemisphere is boosted with an economic bonus, and then one phase where the western hemisphere has an economic bonus (resulting in a clear, territorial disparity between the two that would constantly repeat over time). Obviously, that is a completely random and weird example; I'm sure players would define historically accurate "natural disasters" and permanent resource-based bonuses for specific maps (of course, all of this being completely optional).