Obviously this is an unfinished video - I suspect that Mercedes didn't intend for this to be released to the public. Anyways, that aside, I take issue with the way text messages are handled. Siri dictation rarely works reliably enough to inspire confidence that what you are saying is what will get sent.
I can see this being the source of many a misunderstanding. Even in this video, you're not sure if Siri is sending "I won't be home until eight" or "I won't be home until late". I can foresee far worse things than this, though... being unable to see the messages you are sending (or receiving) will surely be frustrating, resulting in people pulling out their phones while driving in a fit of annoyance to just manually type the message in.
I guess we shall see how this pans out.