Secure sharing — The CarKey feature for iPhone also includes something called Express Mode. That allows you to use your iPhone as a key without first unlocking it with FaceID or your PIN but can be toggled on or off from the Car Key app.
Maps and charging — With iOS 14's updates, Apple's also added a bunch of new features to Maps. In addition to new cycling information for those who don't want to take the car, it's adding information on charging stations and will let users view the status of the car remotely. Apple says the first companies it's working with on these EV-friendly features are Ford and BMW. So while the BMW 5 Series isn't an EV, it sounds likely the key feature will let you do more than just unlock and start the car, but will likely enable you to remotely control the climate control, check your fuel level, and monitor other vehicle details.