I always thought that the dynamic weather in Skyrim should play a more than aesthetic role in the game. It would be great if weather conditions would affect the player in various ways. For example, the harsh blizzard like conditions that can be encountered in the mountains could lower the player's stamina regeneration rate. And if its pouring down rain their attack rate could decrease (due to slippery handles and such).
In a similar way, I found it a little odd that the obviously bone-chilling waters in the northern reaches has no impact on characters. After all, shouldn't swimming with icebergs be unpleasant? Just as there is a time limit on how long you can remain under water before you start to lose health, I think after a certain amount of time of being in frigid waters the player should begin to slowly lose health and stamina.
I don't have the time or skill to implement these sorts of changes (if they're even possible), but it would be nice to see someone help make the weather in Skyrim have a more tangible effect in the game.