Quirks would be a great idea...so long as we, the players, could pick them. I'm not a fan of just adding a bunch of hidden traits and calling it a day. I want quirks to be something that compliments and enhances the traits system the way that the turn on's and turn off's compliment and enhance your sim's base personality in TS2. So, say, if your sim has the traits Gloomy, Bookworm, and Loner, you could add the "Book Shield" (your sim hides their face with their book when reading in public or around other sims in general) to accentuate how bookish and socially awkward they are, the "Distrusts Vegetarians" quirk because in your head cannon your sim believes that all vegetarians are actually evil wererabbits bent on forcing all of humanity to suffer the same meat-free existence their wererabbit biology forces upon them, and the "Knucklecracker" quirk for the sake of giving them an annoying/disturbing habit.
And, of course, you know I'm a fan of more intense negative emotions, extra trait slots, and stronger traits. In fact, add officially patching the game so that Uncomfortable moodlets boost other negative moodlets and add a Stoic trait that makes it harder for a sim to gain higher-level moodlets in any emotion and a Not Easily Impressed trait that greatly reduces the effectiveness of ambient Happy moodlets from decor on your sim. I'd like that a lot.
