Ohh, what a neat idea! :)
Expansion Packs
Get to Work: Ability to run home-businesses/some little businesses for kids. Or completely reworked Aliens.
Get Together: Photo booth.
City Living: Better Apartments + ability to build anywhere.
Cats & Dogs: Separate slots for cats and dogs. (Won't take up a Sim slot).
Seasons: slow-dancing, or kissing booths.
Get Famous: Bands, singers
Island Living: Actual ui for Mermaids with abilities, or house-boats, or at least deeper diving.
Game Packs
Outdoor Retreat: Hiking/Exploring together
Spa Day: *n/a right now*
Dine Out: Ability to be the chef.
Vampires: toddlers and kids develop tiny fangs as they age, limited powers. (toddlers can bite teddy bears, etc; children could maybe be able to learn mind-reading/control)
Parenthood: *n/a right now*
Jungle Adventure: *n/a right now*
StrangerVille: *n/a right now*
Stuff Packs
Luxury Party Stuff: Those big beautiful stairs (big wide curved stairs, or ballroom, split-stairs.)
Perfect Patio Stuff: Gazebo, or hanging chairs.
Cool Kitchen Stuff: *n/a right now*
Spooky Stuff: Trick or Treating... missed opportunity twice! (Sure, we have neighbors being able to come to your house, but your current household cannot go out trick-or treating. :( ). / Ability to create your own haunted houses and you and your Sim getting to go through them.
Movie Hangout Stuff: Sleep-overs "event". Ability to invite guests over story-telling/pillow fights, "truth or dare".
Romantic Garden Stuff: picnic dates
Kids Room Stuff: bunk-beds.
Backyard Stuff: Pool slides, pool water-falls, or pool activities.
Vintage Glamour Stuff: *n/a right now*
Bowling Night Stuff: Pool tables (just more activities for dates)
Fitness Stuff: Climbing rope, or gymnastic bar.
Toddler Stuff: More toddler interactions between other toddlers.
Laundry Day Stuff: Hmmm.. not sure.. I pretty much love everything in the pack, but I am sure there is something that could be added, just don't have anything at the top of my head at the moment.
My First Pet Stuff: More pets. (ie: birds..)
*note* getting sleepy, will update the "n/a" ones later tomorrow. :)