As ineffective as biometric unlocks (TouchID, etc) are in targeted data retrieval scenarios, I'd wager their wider adoption would effectively kill casual smartphone theft.

Every 5S owner I know actually uses TouchID. I'd guess around half of the 5/5C users I see bother to use the four-digit PIN, because it's a longer process to unlock.

Smartphones unattended on a bar will be a less attractive target when the default assumption is that it's locked, and would be a large undertaking to put it into a state useful for the thief's personal use or resale. Making locking convenient enough that everyone does it (and the phone's physical security strong enough that it's an actual ordeal to bypass) would build a herd immunity for smartphone owners.