One thing that's been hard to implement are annual or even monthly events because that can take a looong time in game hours to get to just one of those. I would love to see some weekly events take place. This could also mean the NPC's daily ritual changes on weekends so there would be a weekend script where they go and what they do.
Perhaps the taverns get more crowded on weekends. Also give the NPC's several changes of clothes that they randomize through so on a weekend you might see a woman that works a market tent during the week, wearing some more sixy clothes and hanging out at a tavern.
Street parties on the weekends, maybe even most shops closing on Sunday except for a few that would charge more giving you the option of taking that hit to sell stuff on Sun or wait it out for the next day.