Looks like 4.3 just leaked from a test device's build. Yeah, you'll need to have an unlocked bootloader.
Have at it: Android Central | Android 4.3 build for the Moto X leaks from test device
XDA Link: xda-developers | Moto X T-Mobile System Dump [4.3]
Bugs still apparent but camera performance is reportedly improved [...] They claim that the build seems to be slower than the current Android 4.2.2 that's shipping on the phone, but that the camera seems to be improved over what's available now.
Have at it: Android Central | Android 4.3 build for the Moto X leaks from test device
XDA Link: xda-developers | Moto X T-Mobile System Dump [4.3]