Self-Driving Cars Won’t Just Watch the World—They’ll Watch You.
However, right now the headlines are more hype than they should be. As with all technology the reasons behind it are slightly different than the public reaction.
I've been to a ton of these conferences and they don't really seem to be putting "cameras" but rather sensors. Probably lazer. The reasons behind it I think stem more from speech recognition issues.
I guess no matter what your dialect, your face makes the same shapes when you talk. In car speech recognition is especially bad with cabin noise and everything. So they are looking for ways to improve that. Sensors that watch your face are one of them.
Now - technology does morph into other stuff. But for right now, they aren't really "trying" to spy on you. But, I'm sure eventually they will. It just isn't their initial motivation. (allegedly)