Some ideas I have for that:
-Regular men's clothing.
Jeans, shirts with prints, some hats, regular and balding hairstyles that are not super stylised, some beards too, cargo pants, a nice leather jacket, just stuff you see men wear all the time. Not some weird high fashion stuff. Have a man design this pack, please.
-High tech kit.
Adds futuristic looking electronic devices and appliances like computers, a TV, dishwasher, fridge, toilet, shower, bed, hot tub, washing machine and dryer, new spaceship too, we never got one since the base game.
-Canes.
Since Dust the bust does add a bit of gameplay, I think canes could work for that too, offering few objects but ones that add new walking animations. Like it could add a dozen canes with different colour swatches and a few walking styles to go with it.
Elderly, elegant and swag.
-Goth clothing.
Could be a good theme for a pack with some darker stuff as well as some interesting jewellery, hats, gloves and shoes. Should give as much to men as to women though, they need to stop neglecting men and giving them descent clothes too.
-Cybernetic pack.
Adds tattoos, gloves, glasses, boots, clothing, scars, make up, eyes and such that can make your sim look like they are a cyborg.
-Alien pack.
Focuses on the most neglected life state. Adds several alien suits including the styles seen in sims 2 and 3 as well as a UFO space ship to construct and alien clothing in all categories. So they'd have thematic athletic, sleep and swimwear too.
-Wizard pack.
Since realm of magic was horrible with clothing, offering next to nothing actually looking like something mages would wear, I'd propose a pack that adds some nice wizard fashions. Pointy hats and hoods, long flowing robes with wide sleeves, also the sexier variant for the seductress kind of sorceress. Also of course some hairstyles and impressive beards, maybe old fashioned glasses too and some librarian looking mage outfits.