The whole CarPlay thing feels and sounds like a half-baked idea in the current form. I don't think Apple has it figured out how they want just yet or can't move forward with their vision. A fair portion of the blame for that is the automobile manufacturers. I don't think they even know what anyone wants as far as that kind of integration, nor do they want to test the limits of what is legal (distracted driving laws, etc).
I know I'd be pretty pissed if I were a automobile maker and some idiot with a rooted phone sues me because said idiot got hacked and his car got destroyed/stolen because of it.
My impression is that Apple wants to control the UI of all in dash systems via the iPhone, and the auto manufactures don't like the idea that there would be less hassle moving between a BMW, Volt, and Prius. It feels a lot like what Microsoft tried to do with the X Box One and the cable box. The idea is good, but the people who make the cable boxes and the carrier that bought them want you to be frustrated when you try a different product. That frustration is removed by the X Box One and suddenly there is less friction when switching between Comcast and DirecTV. Cars are so expensive that any feature that increases the likelihood of staying with a manufacture is a good thing, at least to the manufacture.
Remember in the Keynote when they talked about different size dashes no longer being an issue? That was Apple saying there is not really an excuse for buying a new car that doesn't support CarPlay.