Please don't use [NoInterfaceObject] unless there is an actual reason to do so.

Please avoid the .get() and .set() pattern. If you don't have a predefined set of properties, it would be more extensible to just have:

Vehicle.request("speed").then( (result) => { /*process result*/ }); 
Vehicle.set("speed", {/*some values*/}).then(...);
Vehicle.request(["speed", "whatever"]).then(...)

spec says:

As a result of these constraints, this specification shall allow for automobile manufacturer-specific extensions or restrictions. Extensions are only permitted for interfaces that are not already described by this API, and must be implemented to conform within the format and guidelines existing in this specification. If a Property is restricted, the automobile manufacturer would omit the optional feature in their implementation (see the Availability Section).

The above should be avoided, otherwise it's not much of a standard.

For some use cases it might be needed to allow complex data structures in addition to primitives

(see automotive-bg/rsi/protocol/)

Add a recommendation for obtaining authentication and authorization to access services. How to get the JWT or Bearer Tokens named in the viwi.protocol spec?

(see automotive-bg/rsi/protocol/)

Please avoid defining new error types to the platform. Please reuse one of the existing DOM error names:

https://heycam.github.io/webidl/#idl-DOMException-error-names

having vehicle.from/to doesn't make sense on their own. If anything, there should be a vehicle.log object, that contains the start/end date.