Dangerous Stuff - From what I've heard, this is one of those packs that lost to Laundry Day Stuff in a community poll. I have some ideas if they ever decide to bring that back.
Essentially, every base game object has a 'dangerous' or 'risky' alternative to it. Electrical objects will break often and will kill Sims with electricity if they attempt to repair it with low handiness skill. Kitchen objects have a higher chance of breaking and causing fires, even if they don't normally catch on fire like microwaves. Plumbing objects break often, have a higher chance of giving Poseidon's Kiss for ALL sims, and if they break, huge water puddles will spread across the entire lot, breaking any electrical items on the floor around it. CHAOS!
Love is in the air? Wrong! Gas leak. If the risky gas oven is left broken for too long, a gas leak may occur. Your bills might skyrocket, mist will appear on the lot, and Sims will start to notice a terrible smell. Any wrong move will cause anything on the lot to catch on fire. Woohoo in a bed during a gas leak will catch the bed on fire. Electrical items may overheat, break, and cause even more fires. Not enough handiness to fix the oven? More fire for you! The repairman is your friend.
Yeah, basically it's Murphy's Law. Anything that can go wrong, will go wrong with these objects. There'll even be two new traits returning from previous games, Lucky and Unlucky. They're pretty self-explanatory and dying as an unlucky Sim will earn you some sympathy from the Grim Reaper until your time is up. I think there'll also be a number of new dangerous objects as well as clothes that follow a safety theme.
That's the only thing I have in mind for right now. I think it would be really exciting and challenging.