One thing in each? Okay, mine would be:
Get To Work: An Occult Hunter playable career. Something flexible that could be selected for all Occults or just one type. Example: Vampire Hunter, Witch Hunter, Ghost Hunter, or general Supernatural Hunter. I know that Ghosts were the only thing out at the time, but if they went back to add something, this could be it. If this is too complicated, then how about that Grim Reaper career?
Get Together: The ability for Sims to dance together. Not in a performance style like they do now, but facing each other, like real people do. Like when a group of girls go out and hit the dance floor, they sometimes dance in a circle, facing each other. Or if a couple goes out to dance, they usually dance facing each other, not leaving each other to go gawk at the DJ. (Honestly, who does that?)
City Living: Buildable apartments. Or even placeable apartments. I'd even settle for direct replicas of what's in City Living but be able to place them in Newcrest or another map. I just need more living spaces and I really want apartments. It's ridiculous that they're confined to one city.
Cats and Dogs: A toggle for sick pets or gameplay adjustment so that if you're not actively playing a veterinarian they won't get sick at all. I'm really fed up with sick animals everywhere in Brindleton Bay.
Seasons: Hmm. I'd say either foggy days or the ability to delete the premade holidays completely. Or, actually, how about an "ignore holiday" feature for Sims to not get bummed out every single time the player doesn't cater to the holiday. This gets old very, very fast and I may not want to delete the holiday altogether because I may sometimes use it in a different household, but I want to be able to have some Sims ignore Winterfest or Brawl Day or TV Premiere Day or whatever without getting bummed out.
Get Famous: The ability to have normal conversations and build relationships with celebrities. For crying out loud...
Island Living: My God, just one? How about underwater swimming or a secret lot on the other side of the cave with hidden treasure that has a low percentage of being found, or boats that can take multiple Sims, or more Mermaid powers or Mermaid furniture styles made out of seashells, sea glass and seaweed, like a giant oyster bed... any one of those.
Discover University: Add in for term progress to freeze without kicking Sims out of Uni so that rotational players can still switch households and play other stories without the game taking charge of the Uni Sims and making them fail or graduate.