The changing of weather, like rain snow and wind that could effect people and environments. Like if it rains the ground (if dirt or grass) could get slippery and would make it harder to fight, and maybe a certain percentage of R2 swings may slip and miss, or if your running forward and all of a sudden push back on the thumb-stick instead of instantly turning around and running towards the camera the player would slip and fall getting mud on him/her.
Or with wind. Imagine traversing the Valley of Drakes in DkS and having to fight heavy wind that could knock you down or even off the cliff itself if you dont hold your ground while walking (maybe you would have to hold your shield up while against the wind to traverse it properly so if you encounter an enemy you'll have to trade footing for attacks, or something like that.
Or even the changing of seasons that could effect where you can go such as during the winter you could cross a lake that you couldnt normally get across. Things like these ideas could be really interesting a cool if done right.
And much more likely to happen if DkSII is a next gen game.