While it's certainly an interesting demonstration, the only thing it really proves is that when someone has physical access to anything from a phone to a car to your house, all security bets are off.  In fact it's not even a remote exploit. If you are actually connected to the car, you can do anything including reaching under the body with a pair of pliers to crush or cut brake lines. 

Ensuring the security of the electronic systems in cars is critical but so far we haven't seen anything that threatens those systems. At some point it will likely happen somewhere, but we are safe for now.?