I wouldn't buy a car without this. The built-in car nav/interface systems and designs are awful. Obviously, it'll take a little time for CarPlay to develop, so I hope it'll just get better.
I'd like to start to see front-end cameras in cars (and then eventually left and right) in addition to the rear-end cameras that are becoming more and more standard. I could see this being helpful for precision parking, lane changing, and monitoring your vehicle remotely from your phone. Also, if every camera recorded the past hour or so, and then you could download that data onto your phone, that would be huge for car accident reports, because you could just replay exactly what happened.
I can also see "Find my car" just like "Find my iPhone" coming soon, if your car gets stolen, or if you just forget where you parked.