Imagine a game where the plants grow, the rivers flow, and the wind makes waves. There is a species slowly dwindling due to over-hunting because of the value of their hides. As a result of the over hunting, more trees are growing and making shelter for a new creature to thrive. Once the hunters go away for a time, the trails will become overgrown and new creatures will inhabit the area.
All of this is possible with several current games and would greatly increase the experience quality in several games. Predatory creatures could slowly level and grow as they find food or prey. Creature spawn points could be created when a given level of creature comes within range of the opposite sex. Creatures in a neglected area would grow stronger and become elite prey while creatures in a popular area get hunted down, possibly to extinction. Traffic can limit the vegetation and damage it in order to keep trails and paths open.
Vegetation can be triggered to spawn more vegetation and change size / level over time while being effected by collisions, creatures and even fire. Water and wind can be easily scripted into most games with some outstanding effects but the erosion effects would be a processor heavy effect.
Erosion and land effects such as volcanoes and plate movement could simply be applied on a weekly or monthly basis while most plant and animal effects can be scripted into real time effects.
Most of these scripts can be written without much effect on code by use of subroutines and simple rules. The end result is roads made by the players in a world where digital exosphere is in play. The areas would look different when players revisited them and there would be studies based on the behavior and effects caused by use of such code.
In game markets would start to vary based more on supply and demand while the game simply becomes more fun to play.
I have been considering this idea since I discovered during editing video games and maps that I could make units or creatures that level up with kills and spawn other creatures on a predefined trigger. The concept is really quite simple with a few lines of code. Spawn points become unpredictable and populations start to regulate themselves with a little tweaking of the numbers and an occasional limit. By creating a food chain and creatures that grow, the game becomes much more fluid and realistic and that seems to be the point.
There may be a need for rules in some aspects of game play to limit such affects. Small creatures may need to be non target-able until they grow to a certain level so as to keep popular area from rapid extinction and prevent over-hunting. Some creatures should roam and have large areas to migrate across in order to repopulate and for creature feeding purposes also.
I do not know the game mechanics of every game but the scripting of behaviors and zone or map design is quite similar in most of them. This may already be on the idea list for future updates or games but it is possible with the engines we use now. There will be no effect on the user end as far as speed and graphics. The servers are not near their limits for processing power and this would barely effect them anyway.
Let me know if you have any ideas or additions.