I think that TS5 should honestly get rid of moodlets, emotions as they are, and multitasking.
The moodlets were never a good system and it's utterly unnecessary, I can play without them that it's just fine.
The focus on emotion changing and having to achieve a certain emotion to get a certain skill buff also needs to end as well as all emotion requirements. Emotions should be something the sim happens to be feeling and ofc these should heavily impact what the sim does and how he reacts regarding other sims and the world but in TS4 they are more of a tool to achieve certain goals rather than an input on how the sim happens to feel, it pulls focus away from the sim itself and onto the tasks ahead which is not really a good thing.
I think there are too many emotions and too many ways to manipulate them watering down their overall value and impact.
The multitasking...it's pretty great, for playing but not for developing as we have come to see, and it's heavy on the engine. Unless they get a way to make it smoother in both terms I think TS5 should just stick with the casual multitasking of TS2 and TS3 with little touch ups, I honestly wouldn't mind the sacrifice if it meant better everything else.
But you know regarding new features I'd like to see recipe crafting like in TS2 console where you have the ingredients and have to mix them to find recipes, layers of clothing instead of one pieces, that we can mix and match, free-shape pool/fountain tool that lets us do curves and such instead of having separate pieces, better sim genetics, hair/beard growth, etc.