To be honest, I think cars will be added to the game when the time will come. Tho we will not be able to see our Sims actually traveling from destination to destination (which does not bother me. It annoys me in TS3), maybe travelling, especially to certain destinations, will affect the Sims in different ways.
For example - Sims traveling to San Myshuno will get an angry Moodlet because they haven’t found parking lot (a known problem in big cities). Or Sims traveling from Windenburg to Strangeville could get a bored moodlet from the very long drive.
I think it can upgrade the gameplay around cars and traveling in general.
Because we’re not "present" with our Sims while traveling, I think the travel options can be expanded and varied, and can add interest and a little bit depth.
I mean - NO MORE FREE TRAVELING!
Sims who can afford a taxi can get to their destination faster and more pleasantly. Of course the price of the taxi will depend on the distance from destination to another. Your Sims don’t have an extra Simoleons for a taxi? Take a bus - it's cheaper! But also a longer ride!
Maybe Sims who own cars could work as drivers? A kind of Uber service?
I think it can add to the realism of the game. No more Sims being sent from place to place in a second. It’s can also effect on townies, which means no more Bella Goth in EVERY WORLD! what do you think? Do you like my ideas? Let me know (: