Consider that previous hacks of cars have shown that it is possible to take control of the lane assist system in order to turn the car left or right. ans hacks only get better over time, so imagine this, someone is driving on a dangerous road, and they are in the process of making a left turn and at a carefully chosen moment, an attacker engages the lane assist , and makes the car turn right.
No car company will admit to potential flaws, as that is bad for business, and there is no way for them to know in advanced which flaws the system has. No developer programs with the intention of leaving in security flaws. If the car can be remotely connected to, then it will eventually get exploited. The other concern is what happens to older model connected card when the companies no longer want to push out security updates?
Since just like all major operating systems, as much code as possible is reused, this is why new exploits today for windows 10, also work on windows XP. Imagine an exploit being discovered for a new car, and it works on older models, but only newer models receive the patch. Sadly this is the kind of future we are heading to.