So if you've looked at the News tab for the Website, you would have noticed that there is an upcoming 2 year anniversary in-game event, happening from the 4th-10th of April. This in my opinion is a perfect launch pad for Zenimax to start making new in-game events, for particular days and weeks.
This could be from anything like changing rain to snow, at Christmas time, having pumpkins dotted around for Halloween, fireworks in the sky for New years, etc..
Personally I think they should be related to Elder Scrolls Lore and so should be set for Elders Scrolls' dates, making sure immersion is maintained.
What in-game events would you like to see come to the game?