What kind of theme would you like to see added to a stuff pack? Keep in mind, we're only talking about mostly Build/buy and Cas, since it's pretty hard to know what can and can't go in a stuff pack as gameplay objects, plus the gameplay objects don't necessarily always match the build/buy, like Movie Hangout.
Note: I purposefully left off the stuff packs that were in the community vote, but feel free to select them in other

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For Retirement pack I was thinking that the new gameplay object could be Canes and maybe a new board game? Maybe even things like Sewing, knitting, etc.
Lots of antique furniture like rocking chairs, wall/table phones, dial phones, old tv's with antennas etc.
As for cas, a bunch of clothes and hair styles fit for the elderly.
The clothes that come with Teen Stuff would only ever randomly appear on teens, but you can put them on whoever you want yourself.
Gameplay objects could be Skateboarding, Handheld Video game console, cheerleading pom poms, roller skates, functional and genetic acne etc.
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Ideas for a pool pack: Pool bars like in Island Paradise, Water slides, diving boards, water volley ball, marco polo, inflatable chairs, diving rings for games, hold breath competition or the color game. If anyone hasn't heard of the color game it's where you hold someone while in the water and think of a color, if they guess the color wrong you dunk them, if they get it right you set them free.
Sims 1: Hot Date
Sims 2: Seasons
Sims 2: Happy Holiday Stuff
Sims 3: Seasons
Sims 3: 70's, 80's, & 90's Stuff
Sims 4: Seasons
Sims 4: Backyard Stuff
Sims 4: Spa Day Game Pack
Pool Stuff but Weddings and Casinos are a close 2nd and 3rd.
Legacy Photomode
That being said, I'd get all of the packs listed
If they did make an elder-focused SP, I would buy it. I like the idea of giving them a game and I think that casinos could offer an element that appeals to elders since so many of them are drawn to things like bingo and casino games. I'd like to see some clothes that nicely flatter them and as I've mentioned, some softer make up applications that flatter them better. If they want to add some odd hair colors, that's fine too. I think that recent free curly hairstyle that they gave out is one that is very good for elders.
Sure, I'd be interested in a renaissance fair or bed and bath (cough, cough "sleepwear") theme. I'm pretty easily persuaded. I'd actually like voting for SPs again when in doubt. I enjoyed the voting process for Laundry Day even though that wasn't my pick. I'll admit that I've made a lot of use of that pack and I have laundry in any household where it would fit, there are just other things that I'd like to see more.
I'd like to see an Age Filter implemented, similar to the gender filter; have the clothes from Teen Stuff (maybe a few other base game items) limited to only teens but players can remove the filter to dress their Sims in those outfits if they choose, while game generated Sims (especially elders) don't go walking around like rejected extras from High School Musical.
Fun must be always -- Tomas Hertl (San Jose Sharks hockey player)
Great suggestions! I'd love to have an entire cheerleading outfit with multiple swatches to go along with the pom poms so you could set up cheer squads from rival high schools. You could make cheer clubs (groups for base game) that meet after-school and do little routines (routines would be available options when you click on yourself while wearing the outfit). You could make skater clubs too! OMG I need this now
My sims 4 studio with poses for download and stuff: click
But a Future Tech stuff pack could include servos! Maybe it could include a variety of skins and outfits for them, and some smaller functioning robots and they could have a chance to break down and be repaired by a Sim, or upgraded.
Teen stuff would be cool with the right focus. Personally, I'd like a "rebellious" feel to it, with piercings and more punked out hair and clothing styles. I'd love for drums and bass guitar to come in this, with the ability to sync the instruments with singing so they could start a garage band.
Some of these are probably too ambitious, but judging from some of the stuff packs they've made so far, you never know. It could be possible.