The number one place I would want security on my phone, would be at a bar (or party), where someone might take my phone when I'm distracted, and then doing either something innocent ("lol. im gay. party hard!!!") or nasty (transfer $100 to own account), depending how well I know them. This could easily be done within a meter or two of me, without me noticing. Adding some rules could be nice (be in car, charging at home etc), but generally, I would want my phone to be locked unless I'm holding it.
That's what I'm worried about with Touch ID. The new "draw a penis on someone's forehead when they're passed out" is going to be "unlock their iPhone with their finger and post things on their Facebook".
You can do this quite easily with Tasker[0]. At home, you could use the presence of your home wifi network as the indicator that the lock should be disabled, while in your car you could use a passive NFC tag (about 50ยข).
How about proximity + voice print or proximity + face unlock. It's basically 2-factors. Maybe this is the use case for Google Glass, retinal unlock just by looking at the screen.
