I agree that they are likely at least starting to draft cars, only there are a lot of different aspects that would go into it. If it were coming this EP, we'd have been hinted it already. Instead we've got the Tooth-Bear-ie thingie, and anything infant.
When they do do this, I hope they change it so your sims will no longer walk off to the edge of a neighborhood to "go home." At least for the ones who own a vehicle. Instead have them walk to the nearest road and have them "get in" their car. I don't care if the cars just magically appear there when they do this. I think 90% of existing neighborhoods have roads. The only exceptions are Hidden Lots, which are smaller and easier to leave anyways.
I also hope for something similar to the old beat up car you could purchase in TS3 and fix up. I hope they make it so you can open a car selling dealership if you owned the Get To Work pack too.
Another way cars can be streamlined in with other features we have is if you could upgrade cars with new features, perhaps using a new type of vehicle upgrade part, including eco-upgrades with the Eco-Lifestyle pack.