I'd like to see a Hollywood type world with multiple lots. One with a movie, tv studio. A music studio, fashion design, and a modeling agency. Don't know if anyone played the "Movies" game, but I loved it, and still play it a bit. I'd like to see something kinda similar. On the movie studio lot, you can build your own sets, and add props. For any genre; action, sci-fi, horror, drama, even westerns, Have a post production where you can edit, add music, and special effects. Could be a way to get cars :/. Not functional, but at least as props. Pre-made sets can be used, like the hospital room, or detective set from GTW. Of course filming can take place in other worlds. The lot could have trailers for Sim actors to live in while working.
There could be Hall of Fame locations for Sims to visit.
Celebrities can have problems and need rehab for treatment. Addiction is not a thing in the Sims unless it's custom traits or mods. Maybe the Glutton Trait. Make up some addictions for Sims.
Dogs and cats can be trained to act.
A Broadway type theatre for plays.