It's warranted for navigation, or possibly things like virtual mirrors. I wouldn't want to see text messages. Why not just use audio if it's so damned important to get the text?
My jaw hit the floor the first time it went off. My jaw also hit the floor when it read a rather private message while I was a _passenger_ in someone else's car.
Example:
(Phone): New text message from John Smith. Would you like to hear it? (You): Yes. (Phone): "Bla bla text message contents here"
(Your Spouse): Yes.
I think the moto x is an awesome phone but this is indeed a problem :)