Fantastic ideas! So hard to pick just one thing each. Mine would have to be:
Expansions:
Get to Work: Definitely agree with the lemonade stand or I'd have more options to set what kind of retail store your sim owns. (Basically I'd like it to be more like Open for Business if I'm honest, but that's a big ask).
Get Together: For the groups themselves to have more reputations or something more like the social groups or social classes from TS2 Apartment Life.
City Living: Some immersive night clubs or cocktail bars.
Cats & Dogs: Collectable wild pets like in TS3 (birds, lizards etc.) that you can find within the neighbourhoods.
Seasons: Also more collectable bugs in regular neighbourhoods. I'd have liked to see fireflies in summer in worlds outside Granite Falls.
Get Famous: More new careers, like singers and definitely an official DJ or Mixer career rather than just registering with a label.
Island Living: Hammocks. Or access through chance cards to a secret lot via the cave and deep-sea diving. I can't choose!
Game packs:
Outdoor Retreat: An actual hiking rabbit hole with chance cards rather than just walking about the neighbourhood, like in JA when travelling through the jungle gates or the old Bon Voyage day trips.
Spa Day: The option to have a masseuse skill and potentially run a spa if Get to Work is installed.
Dine Out: Option to assign yourself as a chef/waiter/host. Especially with multiple family members in one household so they can all make themselves useful.
Vampires: The ability to hunt in packs.
Parenthood: After school clubs.
Jungle Adventure: Archaeologist career with an excavator or historian branch once you hit level 5.
StrangerVille: More lots!
Stuff packs:
Luxury Party Stuff: Nectar parties.
Perfect Patio Stuff: Greater variety of hot tubs.
Cool Kitchen Stuff: Juice machine!
Spooky Stuff: Ability to use Spooky Stuff items as Spookfest costumes with Seasons installed.
Movie Hangout Stuff: A bigger popcorn machine. Like the big, old vintage corn poppers on wheels.
Romantic Garden Stuff: More romance interactions.
Kids Room Stuff: Bunk or pull-out sofa beds!
Backyard Stuff: Group games like volleyball or pool games.
Vintage Glamour Stuff: Probably just add more vintage-themed furniture.
Bowling Night Stuff: Slush machine.
Fitness Stuff: Interaction to take fitness classes at the gym with the option to instruct classes for simoleons once you reach a certain fitness level.
Toddler Stuff: Daycare career.
Laundry Day Stuff: Option to perform mischief interactions on the laundry line like tearing down clothes.
My First Pet Stuff: Birds! Disappointed we could buy rodent cages but not bird cages.