I'd personally want a sci-fi or medieval kit. Realistically, sci-fi would have a decor theme that's similar to Get to Work's Scientist items. Maybe even throw in some futuristic outfits and glowing accessories. Medieval would include some peasant or royalty clothes alongside display swords. Couple that with Horse Ranch and you might finally have yourself a bargain bin version of The Sims Medieval.
Ideally, despite Bust the Dust's broken state, I wouldn't mind seeing a sliver of gameplay from future kits as long as it's tuned properly.