We had known the Moto X was going to arrive with a locked bootloader. But on the flip side of that, it was previously announced that majority of the carriers would allow users to unlock the bootloader should they want to go that route. Anyway, with that in mind, it looks like the Motorola website has already been updated to reflect the T-Mobile availability.
Basically, at this point the Moto X bootloader can be unlocked by US customers with T-Mobile, US Cellular and Sprint. Looking at the other side, that leaves those with an AT&T or Verizon Wireless branded Moto X stuck with a locked bootloader. That being said, if you happen to have a T-Mobile, US Cellular or Sprint branded Moto X and are looking to unlock the bootloader -- you can head to this Motorola page to get the process started.
In addition to the already available Moto X models, those in the US should soon also have a few developer models to choose from. Those models look to include one with general North American support (for T-Mobile and AT&T) and the other being narrowed down to Verizon Wireless support. And just to clarify, those developer edition models will have an unlocked bootloader.
Simply put, if you are a Verizon or AT&T customer and want/need an unlocked bootloader -- you should begin looking towards these developer editions. With that, while being able to unlock the bootloader means more playing around, we do have to wonder what users will be gaining (or losing) in terms of features should they have a Moto X loaded up with a custom ROM.