I think they should add cars, they don't serve much use in a world where you can teleport anywhere instantly but it will be a nice touch and and it will add more details and realism to the sims4.
They don't have to update the worlds, just have them work like the rocket ships where you can place them on a parking lot. You could add stuff like a car mechanic skill where you could upgrade and tune your car and you could have a world where you could race with other sims. You could have different car races for different types of car, you could have races for simple older cars and then more expensive high-end sport cars.
I mean, the boats in sulani don't serve much of a purpose in other worlds either so I don't see why they can't have a car world added to the game.