I def would love a Farming pack to the core,
but mostly I'm feeling for an mega Cultural/International Pack - I can imagine lifestates inspired by various folklores, New Family interactions (Asking for a sims hand in marriage, Marriage life advice, New spouse doing a customary dance for sim, Family can agree and Object, Maybe do quests to prove themselves worthy ;), Age Rites of Passage customs? Ceremonies, Sims carrying jars of water on heads, Toddlers being carried on back cloths, Homeschooling.
Wrestling for a spouse or some drama,
Traditional clothing
Careers could be: Chieftain, Farmer, Midwifery?, Chosen One, Blacksmith, Merchant, Tailor, Dancer, Shaman, Hunter? Children could maybe play tag or have some safe swordfighting, Maybe sims could make perfumes? or Dyes for clothing?
Instead of sims mourning, maybe they could do ancestral worship? Maybe when sim dies they will become a deity or something based on the folklore?