Although this likely comes as no shock to anyone in the mobile world, AT&T has issued a public statement categorically denying support for unlocked bootloaders on any of their devices from now on. Technically, this is nothing new. AT&T has never officially supported unlocked bootloaders on their devices. In this instance, this was a direct response to someone's question regarding the bootloader of the new Moto X. Here was their response.
Ultimately the folks who want to flash ROMs on their devices will find a way to get them unlocked and won't really care about support from AT&T. Still, it's worth noting that AT&T is so draconian about it. It's a debate that seems to go on ad infinitum.To ensure a safe and consistent experience on your wireless device, we do not support unlocked bootloaders.
Source: MotoXForum via AndroidPolice