Another step towards the future where we do not own our cars. I'm not entirely opposed to the idea, depending on how it's implemented (and priced) but I wish they'd be up-front about it.
While I can think of certain things that you might want to be able to do hands-free, these are mostly activities that don't have anything to do with the car itself. Hands-free radio controls, hands-free mobile calling etc. And I'd prefer that these features not be integrated into the car in a way that I can't choose to buy a car with, say, a different radio that doesn't have those features.
In other words, I can't think of a reason that a car should necessarily come pre-installed with any sort of microphone what-so-ever.
But the idea that there is not only a microphone, but that it is sending what it picks up to some remote server, is a notion that I am deeply uncomfortable with.
Most people view the inside of their car as being somewhat akin to the inside of their home. While people might expect less privacy in a car than in their homes, there is still an expectation of privacy to a degree. And that privacy expectation is typically more auditory than visual (of course you can get tinted windows but people expect you might be able to see inside of a car, but not necessary hear what two people are saying to one another).
More likely that if we ever have cars that are safely autonomous, they will be kept scarce by a monopoly or oligopoly of companies who will have one-sided insight into the costs and demands and extract maximum prices from users. Similar to the games we're witnessing being played by large rental property owners.
But perhaps the day will come where some upstart company will begin producing cars that don't spy on you. You never know.