What about the ability to track a phone/tablet after it is factory reset, and then reconnected to the Google Play Services (i.e. identification by IMEI, MAC and serial number).
If this is an invasion of privacy, then generate a unique code number which can be supplied to police in order for them to interrogate Google about the new owners identify.
Problem is that police just don't care. This is why Google needs to step in and make it terms of the Google Play Services that you can't use a stolen phone.