Buried in this CES press release from Audi:

Another innovation presented by Audi at CES is the Audi mobile key. Here, a smartphone or a smartwatch provides access to the vehicle, making them highly flexible complements to existing keys. The mobile key uses Near Field Communication (NFC), which is available even when the mobile device’s battery is empty.

Imagine if a standard emerged that allowed Apple to embed your specific car key in your iPhone and Apple Watch. Approach your car with your iPhone in your pocket and the car automatically unlocks.

Want to open the trunk, or perform a more specific function? Tap a button on your Apple Watch auto app.

No technical reason this can’t be done. And the organization of an industry to follow an OS-specific standard is something at which Apple truly excels.