Voice command may reach maturity very soon also.
That will make life in a cubicle farm really interesting with everyone yelling at their computer. Even if everyone is wearing a headset, the murmur will be as obnoxious as in customer service call center.
Come on now....A bit of exaggeration here, wouldn't you say?!
1st -> Cubicle farm? I'm in my office or study with the door closed if need be. Lol! I can understand -> "What's that?" -> "Oh, that's just grandpa talking to his computer".

We don't wonder at people walking around with smart phone Bluetooth headsets, do we? Not real commonplace, but a reality today. It'll be the same with speaking navigation. Mark my words. Besides, this greatly aids the less-fortunate handicapped.
2nd -> Yell? No one needs to yell, just speak at a regular volume. Who needs to yell?
3rd -> Call center? Do you hang around in call centers? I don't know anyone that does that as a regular pastime.

Not only in an office or study, but if one is in a restaurant, coffee shop, bar, etc. people are "mumuring" already, so what's the difference if one is speaking to a device for navigation?
I was old enough to see the debut of 2001: A Space Odyssey in 1968 as a teenager. No one thought it odd that Dave was talking to HAL. We thought it possible. This is before PC was even an acronym. We didn't think it possible that a machine could take control some day. Or is it?
I don't know about anyone else, but I think anything to be possible when we humans put our minds to it.