USB Restricted Mode was outlined this morning by Elcomsoft after testing confirmed that the feature has indeed been enabled. In Elcomsoft's experience, after an iPhone or iPad has been updated to iOS 11.4 if it hasn't been unlocked or connected to a paired computer in the last seven days using a passcode, the Lightning port is useless for data access and limited to charging.
"At this point, it is still unclear whether the USB port is blocked if the device has not been unlocked with a passcode for seven consecutive days; if the device has not been unlocked at all (password or biometrics); or if the device has not been unlocked or connected to a trusted USB device or computer", reports Elcomsoft.
"In our test, we were able to confirm the USB lock after the device has been left idle for seven days. During this period, we have not tried to unlock the device with Touch ID or connect it to a paired USB device. What we do know, however, is that after the seven days the Lightning port is only good for charging."
The point about this is not that Apple is protecting law enforcement snooping, it is working to stop police in an active investigation who have seized a phone using a warrant from breaking into a phone.