I doubt that cars, if they ever come, would be drivable like in TS3. I would be satisfied if they were like a cross between those in TS2 and Freetime, and the car from Roaring Heights. They could require a driveway object (not a garage), which wouldn’t be too big. If the lot was not adjacent to a road then there could be a restriction preventing the placement of a car. (No cars in Sulani or on the Island of Windenburg, but I wouldn’t want them there anyway).
On the home lot, cars could be worked on and fixed as a new skilling object, be used by teens for parking and making out (with radios playing etc), and serve as a new woohoo spot for adults. Teens would still have to learn to drive to access a car but this would likely be a rabbit hole with chance cards — it could still be done well. It could require some skill and a focussed mood or there could be consequences (like with the rocket ship crash).
For drivers, cars could trigger loading screens (once Sims were inside) but much faster than the phone does, which usually requires a sim to walk to a departure point. However, unlike with the elevators in City Living, I see no reason why they couldn’t (as was done in TS2) animate sims getting in the car together, visibly starting the engine, doing a shoulder check and backing up, at least a little, before the loading screen kicks in. Upon arrival, if there is no parking space object available, the car just goes in the driver’s inventory like in TS3 (and it never gets left behind, unlike in TS3).
I love the idea bikes and skateboards — yes please, along with scooters, motorbikes and mopeds.