Sorry, your phone does NOT send an MP4 video stream to the vehicle. If it were just a video stream there wouldn't be an ability to process inputs from the Wing. While I agree the client (Goldwing) side of the application is relatively simple, it still receives data from and sends data to your phone. Which makes it a client/server application. If you like more information about Google Android Auto technology, HERE is the place to start.The AA app on the GW (or any vehicle, for that matter) is rather “dumb”. It doesn’t actually run any of your apps, directly. ALL of the processing occurs on your phone, which then sends a MP4 video stream to the vehicle. The Vehicle is only responsible for displaying the video stream.
Any limitations on what content you can display is entirely enforced by the phone. Nothing prevents you from sideloading your own .apk that displays radar via AA. Same is true with CP — you can write your own app and deploy it to your phone. However, both the Google Play Store and Apple App Store have policies that prohibit certain types of apps from being offered via those markets — and no radar app has yet made it through approval, afaik.