The sims DO sort of get the loyal trait, if they have a high enough relationship bar. Both my married sims get the "faithful" moodlet around their spouse (the text when you hover over the moodlet says something about your sim takes pride in remaining loyal to their loved one). They don't even seem to flirt with other sims autonomously after this began appearing.
I love the "Always has to be right"/"Always has to have the final word"-trait. Would give it to a lot of my sims (and, finally, be able to create my sim self! Lol)
Can't remember if there is a "Hot headed" trait - if not, I would love that.
Other traits that would be great: "Anxious" - afraid of socializing, afraid of the weather, afraid of strangers, afraid of dogs - you name it. "Paranoid" - constantly suspecting others of wrong-doing, spying on neighbours etc. A general "geek" trait - would make your sim extremely interested in their hobbies, rather wanting to collect stones or play chess than socializing. Would also be cool if this included the ability to make skills faster, but make friends/relationships slower.
