I have a few ideas that Google could implement. Make it an option to have a password in the bootloader to where you can't enter recovery,fastboot unlock, or enter recovery without the password. Obviously if your bootloader is unlocked than it's an open house for thrives
Another option would be to have your emei/ESN attached to Google play services so if a their were to factory reset they could not use Google services with out the password. So if a their were to factory reset or flash a ROM they would have a Google less phone. And as we all know not many people would want a galaxy phone with out ability to use apps. Basically covert a $800 Note 3 into a glorified dumb/feature phone.
Of course neither is full proof with JTAG or changing imeis but why not make it as difficult as possible for some either invade privacy of phone or whipe it to resell...
People who say don't loose your phone... Yeah because when a person loses there phone they do it on purpose or purposely let someone steal there property because YOLO...that's like saying people should just not get into a car accident....humans are prone to errors we are not robots. We aren't perfect nor computers. We have personalities