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ASUS is apparently killing the ability to root present and future Zenfone, Updated
(www.androidauthority.com)
This is a most excellent place for technology news and articles.
Also, something I don't see people discuss enough: for security, you also need to be able to re-lock the bootloader after installing a custom ROM. Otherwise anyone can inject code into the system partition if they have physical access to your device, which would also compromise your encrypted storage. So if there's no way to reverse the bootloader unlocking, that's also bad.