Based on the description for how the sharing would work ("share the video *link*"), I think this is only going to work with whatever apps end up shipping with the Theater feature. So you'd be able to pull up a Netflix video on your phone and share the link to it with your car and it would start playing in the car. But it's not going to be something like AirPlay where you can share almost any video or mirror your screen.The sharing video to the car is a game changer. That's essentially the same as casting. How awesome!!!
Down boy, down.
This is all still "early access" stuff - not for the rest of us.... please be patient.