It's a XX Thousand dollar car, and you are pondering about a 300 dollar gadget can operate the car.
Why not just build it into the car, and not tie it to any brand of gadget?
Why would it have to be tied to a brand? I'm sure Android Wear can support that sort of technology as well. It's really not different than keyless entry cars now that use the key fob's proximity to allow you access to the car. My Prius does this now and I'm sure the key fob cost a lot less than $300.