I want web apps to be able to work in other contexts (like car displays)

Having the ability to promote a web app into a car display (e.g. Android Auto, Apple CarPlay) would help make the web even more capable.

Perhaps we could have a property in the Web App Manifest stating that the app is appropriate for contexts like this. Perhaps we could have a CSS media query that checks if the app is running in "auto mode", so that developers can make the UI more driver friendly.
Perhaps we could even have a JavaScript API that triggers an event when the car starts or stops moving so developers can disable certain features that are dangerous while the car is in motion (e.g., disabling the video element unless the user has specified they are a passenger).