I think for those of us who are "long game" players, sticking with a playthrough for more than a game year, it would be nice to have some annual events to look forward to. Perhaps opening a very brief window for certain quests or quest stages to take place. I'll give some examples but I'm certain the folks who make "Winter Sun" or other potentially relevant mods could come up with even better ones:
- Summer solstice boat race from Windhelm to Solitude.
- Armor crafting festival in Whiterun hosted at the Skyforge
- Winter Solstice Feast
- High holy day(s) of each of the divines, when followers (above a certain level) get some awesome boon
- "Magic Fair" at the college in Winterhold, where apprentices compete with their projects
- Dragon's Moot, on the anniversary of Alduin's defeat (tens converge on the Throat of the World)
Anyway, it would be nice to have an event of two every month to look forward to and perhaps prepare for.