I know I already made my list and I want to acknowledge that I'm aware that I specifically chose some complicated base game adjustments. But here's my more "short term" list of things that could come in a pack release. (Just in case the base game is stuck where it is and I can't get my wishes, lol.)
1. Fears and Flaws. Okay, I know I put this in my last post but instead of this requiring the long, complicated process of adding an actual Fear emotion, this would be a system similar to the Vampire weaknesses where we could choose from a grid and it would affect Sim behavior and reactions. Yes, it would be recycling a feature, but a great feature nonetheless. Recycling can be your friend. As long as behaviors and animations actually played out in response the way Vampires do to their weaknesses, this could make the game much more interesting. But I have to add that I still really, really think that Fear emotion should be put in. The emotions remain unfinished without it.
2. Werewolves! Please, please, pretty please? With snouts on top? I want snouted Werewolves with fur and claws. But they should also have the normal, human Sim form too. Maybe at night they automatically shapeshift but you can earn skill points to control it more. They could have a Carnivorous trait and be immune to angry death. They should have options to be "pack oriented" or "lone wolf" (aspirations?) They should have a special affinity with canines for those who have Cats and Dogs. They definitely should be able to fight each other (and Vampires!) and have a Rank system for becoming Alpha Wolf. I think there should be special "pack" interactions and behaviors. I kind of picture them being tribal, with a drum circle, howling together at the moon. In hybrid form, their Fitness levels should buff so they are more difficult to beat in a fight. Maybe they could have heightened senses, have natural affinities for outdoorsy skills and traits, and shorter tempers. The gameplay could include the inner struggle of keeping the Beast inside because Sims would react negatively (Here's where Fear comes in. ;) ) to the Beast Form. So, for example, a Werewolf in college would have to keep his temper down, maintain his Hunger rating (meat!), and not stray too far from the outdoors or he would start to become in danger of shifting from the stress. Of course, the higher Rank they earn, the more they can control it.
I know that Sims 4 is more cartoony, but I'm just going to put this video here to show that animalistic features can be done in CAS. Of course, I'd prefer them a little toothier and more fierce with more feature options, and the devs could fine tune it, but this is the closest I've found to what could still be a flexible CAS for their physical features.
https://youtu.be/N7H_67g7xiM
3. Oh, the last one is so hard to choose! But I've decided to go with ...SuperSims! (I know, not a fan favorite.) But hear me out. If you have Superheroes, you need to have crime, or else there's nothing too "Super" about them. We've had Superheroes and Villains in Sims 2 at the top of certain careers and I always wanted to be able to do more with them. But imagine having crimes in the game. We have no active police so what are Sims to do? Use the Llama symbol and call Captain Llama and her sidekick The Freezer Bunny, to save you! Lol. I just think that San Myshuno would be so much more interesting if you could witness a purse snatching or a thief crawling out a window, or a dog kidnapping. The crimes wouldn't have to be graphic or violent, they should retain the classic Sims humor. Maybe a criminal jumps down into a sewer to escape and if you follow, you end up in a secret lot to take them down. We could have a new big urban city (with cars and stuff!) and the build/buy would have secret headquarters items. And, you know, we could actually put to use that "Villainy" major in University. ;) I'd love to have a Supervillain who sends their minions to cause crime around the neighborhood and steals candy from toddlers and taunts the elderly and steals and breaks things and causes misery until their Nemesis Hero comes to stop them, lol.