It's worth pointing out that if you would like to immediately require authorisation for USB accessories, you can do the same trick that disables Face ID and Touch ID temporaily: simply hold down the side buttons until the "Slide to power off" screen appears. As now implemented, the feature is even more restrictive: When turned on, it will "prevent USB accessories from connecting when your [iPhone/iPad] has been locked for more than an hour". Interestingly, as per the researchers, authorities and private companies don't need any specific USB accessory to reset the counter.
The new feature will not prevent the phone from being charged, but if you want to unlock or transfer any data to or from the device, you will need to enter the phone's passcode on the touchscreen.
Of course, this only works if the device hadn't entered in USB Restricted Mode by the time the police obtained it. The resetting of the built-in feature works even with an untrusted USB accessory, one that has never been paired with the device before.
At any rate, USB Restricted Mode functions by preventing USB devices from connecting to your iPhone or iPad, and yes, that includes Lightning-powered accessories.
The research team isn't sure if third-party adaptors have a similar effect, but this same method can't be achieved with Apple's Lightning to 3.5mm adaptor. "In other words, we have found no obvious way to break USB Restricted Mode once it is already engaged".
iOS 11.4.1 should improve the reliability of AirPods, along with syncing Mail, Contacts, and Noes with Exchange accounts. watchOS 4.3.2 and tvOS 11.4.1 should just have general fixes and improvements. Law enforcement and private companies could leverage the loophole and design new hardware to continue to crack passcodes through the Lightning port. However, this doesn't mean that the USB connectivity with an Apple device is entirely safe.