Natural disasters. At any given moment, an earthquake can strike possibly destroying houses and splitting your town, luckily a tree falls over the gap and there's still a way to cross it, but you have to do a balance minigame with the balance board every time you want to cross it, and if you fail, you die and your file is instantly erased. An asteroid hitting and destroying everything should also be a very real small possibility, like real life. Strong winds can make your hat fly off so don't wear a hat when it's windy. Ability to look out your window while in your house, and the ability to spy on your neighbours through their windows, but don't get caught! You can uncover mysteries by spying and stalking people, and find murderers, and even frame people.
Townsfolk can die, funerals are held, titled "fun-erals" where everyone gathers around trading fruit and designs and KK Slider plays.
Ability to murder people. Invite them over to see your axe collection in the basement and chop them up into little bits, sprinkling them all over the beach, BUT, anyone entering your town may find dead body parts while fishing, then have the option to either alert the cops (which triggers a running minigame that goes on FOREVER requiring you to shake the wii remote, whenever you stop the police catch you and your file is erased instantly.) Otherwise you can kill the other player yourself. A game of scissors paper rock ensues and the loser is brutally killed in a graphic animation and their file is also erased.
You can get in relationships with other townsfolk (no *** relationships) and make babies (see). If you play the game for 9 months or so a baby comes in the mail and can be traded for bells at nooks. If you play the game for another 15 years the boy or girl will break free of slavery and come and kill you, erasing your file. If you choose to keep the child (LOL! yeah right) you have the option to use it in a nice meal (this would work well with Bills cooking idea) or just hang it on the wall. No sex scenes though because I don't want it to be rated T or higher.
I've got heaps more but i've gotta jet for now.