Such a system existed in WoW, as difficult as it may seem, it makes the game experience look less static, for example: after ten million hours of playing the game, just when you think you've had it with dragons and with all the same events and can't find something new for yourself, just then, it's a holiday, suddenly there's a fair in town, or the cities are being decorated in celebration for the ones that fell in battle in order to honor their deaths and celebrate their victory.
Think how cool it would seem to have a day marked in the calender the day you've beaten the great big ugly dragon-god, I'm sure Skyrim would be thankful. Plus, if the whole world was in danger and you managed to save it from ruins, then I'm sure (logicaly) everyone would celebrate that said day (think Independence-Day).
It could be accomplished by providing the game with a calender, forcing events to happen during a certain day or along several days. Making the events trigger active when a certain day of the year comes along.
Let's say for instance, that it could also give you a chance making friends with people and knowing the culture and history of Skyrim better, with actual actions and not just static lore.