if you equip certain items, you unlock hidden quests. I think there are tons but they are like holiday events, appear only at certain times and days....there's what 7,000 item combinations? You'd need to spend years trying to map them all out. There are 105 products, you'd need to experiment wearing each product for a full week with different item combinations, chances are you need to complete certain quests in the game too. So after completing every quest aquiring every item in the game, you'd need to go one by one, changing items and wearing them for a week....I know some quests you don't weild weapons for, so there might just be an infinate number of hidden quests...figure 7,000 item combinations, divided by, 52 combinations per year, works out to 280 years, and if you get 280 people to trying to find them, take about a year.
edit-you'd need to divide it evenly between all 280 people, thats 25 combinations, thats with items in every slot, not including the empty slots.