I think it could be neat to see a stuff pack that really lets you transform your sims house into a place of mystery. Like they are a secret agent, evil genius, super hero or just someone who likes to pretend they are. 

The pack would contain several bookcases with a hidden passage, a breakable wall, trap doors with a slide leading to the room below, a chair with a trap door under it, doors that need sims to carry a keycard in their inventory or require another means of identification, safes, alarms, traps, etc. 

Any other furniture included would just be to be in the same style to not make the special objects stand out. Like you get a regular chair version of the one with the trap door under it. 

But here's a bit more detail about some objects I have in mind for this: 

-Trap door. A 1x1 tile you put on a floor that requires a room or basement below it, there's a tube that goes halfway down the floor. Sims can willingly go through it causing them to land on their feet, but they land on their butt if they got caught by surprise. It can't be triggered by toddlers and infants, but children and up can. It is also possible to put a pool below it, causing the sim to land in the water. You'd be free to design the room sims end up in though. Could be a prison, a secret lab, a man cave, the garage, etc. 

-Trap chair. It can be put above the trap door, allowing it to be triggered by one of the chair options, which has animations to ditch the occupant through the trap door below. But there are a few other options as well like iron restraints trapping the sim sitting in it. Strong enough sims, vampires and werewolves could break out of it on their own. Other sims are able to play several pranks on the prisoner or ask them questions, but can also just release them. 

-Breakable wall. Found under construction, you can place it as part of a wall. It's 2 spaces wide. If a sim has a hammer, they can break down the wall. But spells, a lightsaber or some other items from other expansions could also break it. It can be used to give sims a chance to escape from a prison, put a hidden chamber somewhere possibly with a slumbering vampire, etc. In broken state the wall can also be repaired, walled back up. Can also be fun to create a house that needs to be fixed up. 

-Various secret doors. A book case, a fireplace, maybe behind a waterfall too or through a dresser or fridge. 

-Fireman pole. Like Batman has, great to put behind that secret door. 

-Security door that requires a key card. The key card is an item sims can have in their inventory, you can distribute them as you see fit. Any sim who has a key card in their inventory can put it against a scanner at the side of the door and it opens with a bleep. Sims can try to pickpocket key cards too, if you tell them to do that though now kleptomaniac sims have something interesting they might randomly obtain too that other sims will miss. No one can get in without a key card. 

-Security door that scans DNA. When you set one sim who can enter this, all sims who are related to them by blood can too. You can always set it to another sim if you like, but the idea is that it's something only family can enter. You can put interesting secrets behind it, left behind by older generations. 

-Safe door. A thick safe door that requires a sim to enter the combination. You can select them entering the right combination, making a wild guess which won't open it, or try to crack the code like a burglar. 

-Safes of various sizes. Smaller, sims can put some objects in there they find important. Having a safe could be the trigger needed to enable burglars trying to enter, just like having a washing machine causes laundry to be done. So if you don't want burglars, don't get a safe. Burglars can try to break open the safe and steal what's inside. It's possible to prank whoever opens it too with like confetti or something else that makes them a mess. 

-Security lasers. Full mission impossible style, sims can try to move past it but their athletic skill needs to be high enough. An alarm triggers if they hit a laser, and they won't get past. They can try again. 

-Security alarm. Just a standard burglar alarm as there has been in previous games that triggers a police response. If you put it in a room with security lasers, security doors or a safe, the police will also be triggered if someone fails to get past them. 

-Hibernation pod. A sim can get frozen in here, causing their needs to stay filled up and they will not age, they are effectively removed from the household and they can only be woken up if there's room in the current household. Relationships do persist, the hibernating sim is not forgotten, just for all purposes an NPC. 

-Elevator. Just a regular elevator, but there can also be secret elevators that are small, only holding one person. Maybe like a tube from Sims 3 into the future too. 

-Cargo elevator. For a dramatic entrance, this is a bigger elevator that is a platform raised up or down. When it's down, the roof is closed, it only opens when it comes up. You can put things on this elevator like a couch or other stuff, even a bed. Like it could just be a hidden room under the floor that you can bring up. Which could be great for a dance floor too, or a hot tub or whatever you might like. 

-Stairs that can become a slide. You can switch it when you want, turning it into a slide. This one can only be straight. You can also use it to build your own larger playground, now sims can slide from one floor down to another. 

-Climbing rope. A simple way to move between different floors, sims can slide down the rope or climb up. Climbing up trains their athletic skill and they require 6 points in athletic before they can climb up successfully, and higher than that makes them climb up faster. The rope can also be used to swing into a pool or otherwise play with it, hanging upside down and such. 

-Underwater door. it's a 2x2 square object with a door on two of it's sides, which sims can use to travel between a dry and water area. Great for a secret room in the pool. It does take a little while for the sim to move through it, because it takes time for the area in between to either be emptied with water or filled with it. 

I think it could be neat to see a stuff pack that really lets you transform your sims house into a place of mystery. Like they are a secret agent, evil genius, super hero or just someone who likes to pretend they are. 

The pack would contain several bookcases with a hidden passage, a breakable wall, trap doors with a slide leading to the room below, a chair with a trap door under it, doors that need sims to carry a keycard in their inventory or require another means of identification, safes, alarms, traps, etc. 

Any other furniture included would just be to be in the same style to not make the special objects stand out. Like you get a regular chair version of the one with the trap door under it. 

But here's a bit more detail about some objects I have in mind for this: 

-Trap door. A 1x1 tile you put on a floor that requires a room or basement below it, there's a tube that goes halfway down the floor. Sims can willingly go through it causing them to land on their feet, but they land on their butt if they got caught by surprise. It can't be triggered by toddlers and infants, but children and up can. It is also possible to put a pool below it, causing the sim to land in the water. You'd be free to design the room sims end up in though. Could be a prison, a secret lab, a man cave, the garage, etc. 

-Trap chair. It can be put above the trap door, allowing it to be triggered by one of the chair options, which has animations to ditch the occupant through the trap door below. But there are a few other options as well like iron restraints trapping the sim sitting in it. Strong enough sims, vampires and werewolves could break out of it on their own. Other sims are able to play several pranks on the prisoner or ask them questions, but can also just release them. 

-Breakable wall. Found under construction, you can place it as part of a wall. It's 2 spaces wide. If a sim has a hammer, they can break down the wall. But spells, a lightsaber or some other items from other expansions could also break it. It can be used to give sims a chance to escape from a prison, put a hidden chamber somewhere possibly with a slumbering vampire, etc. In broken state the wall can also be repaired, walled back up. Can also be fun to create a house that needs to be fixed up. 

-Various secret doors. A book case, a fireplace, maybe behind a waterfall too or through a dresser or fridge. 

-Fireman pole. Like Batman has, great to put behind that secret door. 

-Security door that requires a key card. The key card is an item sims can have in their inventory, you can distribute them as you see fit. Any sim who has a key card in their inventory can put it against a scanner at the side of the door and it opens with a bleep. Sims can try to pickpocket key cards too, if you tell them to do that though now kleptomaniac sims have something interesting they might randomly obtain too that other sims will miss. No one can get in without a key card. 

-Security door that scans DNA. When you set one sim who can enter this, all sims who are related to them by blood can too. You can always set it to another sim if you like, but the idea is that it's something only family can enter. You can put interesting secrets behind it, left behind by older generations. 

-Safe door. A thick safe door that requires a sim to enter the combination. You can select them entering the right combination, making a wild guess which won't open it, or try to crack the code like a burglar. 

-Safes of various sizes. Smaller, sims can put some objects in there they find important. Having a safe could be the trigger needed to enable burglars trying to enter, just like having a washing machine causes laundry to be done. So if you don't want burglars, don't get a safe. Burglars can try to break open the safe and steal what's inside. It's possible to prank whoever opens it too with like confetti or something else that makes them a mess. 

-Security lasers. Full mission impossible style, sims can try to move past it but their athletic skill needs to be high enough. An alarm triggers if they hit a laser, and they won't get past. They can try again. 

-Security alarm. Just a standard burglar alarm as there has been in previous games that triggers a police response. If you put it in a room with security lasers, security doors or a safe, the police will also be triggered if someone fails to get past them. 

-Hibernation pod. A sim can get frozen in here, causing their needs to stay filled up and they will not age, they are effectively removed from the household and they can only be woken up if there's room in the current household. Relationships do persist, the hibernating sim is not forgotten, just for all purposes an NPC. 

-Elevator. Just a regular elevator, but there can also be secret elevators that are small, only holding one person. Maybe like a tube from Sims 3 into the future too. 

-Cargo elevator. For a dramatic entrance, this is a bigger elevator that is a platform raised up or down. When it's down, the roof is closed, it only opens when it comes up. You can put things on this elevator like a couch or other stuff, even a bed. Like it could just be a hidden room under the floor that you can bring up. Which could be great for a dance floor too, or a hot tub or whatever you might like. 

-Stairs that can become a slide. You can switch it when you want, turning it into a slide. This one can only be straight. You can also use it to build your own larger playground, now sims can slide from one floor down to another. 

-Climbing rope. A simple way to move between different floors, sims can slide down the rope or climb up. Climbing up trains their athletic skill and they require 6 points in athletic before they can climb up successfully, and higher than that makes them climb up faster. The rope can also be used to swing into a pool or otherwise play with it, hanging upside down and such. 

-Underwater door. it's a 2x2 square object with a door on two of it's sides, which sims can use to travel between a dry and water area. Great for a secret room in the pool. It does take a little while for the sim to move through it, because it takes time for the area in between to either be emptied with water or filled with it.