Couldn't this just be as simple as Pandora not having added Carplay functionality into their app yet, or Apple not giving them the option to do it ahead of the announcement?
It's not like every app out there was compatible with Airplay the day that was announced, only certain apps were. This could be the same thing, the app makers need to update their app to support it, and wait until Apple approves it, and then it will work too.
Now that being said I'm sure Apple will be a little more restrictive on what apps they allow to integrate Carplay into. For example I'm guessing they won't approve video playing or game apps to work with it, becuase they don't want people trying to watch videos or play games on their car's head unit.
That said I think it could be really cool if they allowed video playing apps to connect just to play the audio and give you control of pause/play etc. That way you could have an iphone/ipad the back with the kids and play the movie's audio through the stereo. It would be even cooler if you could sync the video playback through multiple devices. Say each kid has their own ipad/iphone but you could play the same movie on all of them at the same time synced up and playing the audio over the car stereo.
