The holiday themed boot animation should automatically come up for Moto X owners who are running the KitKat update. Moto G owners though, will need to update the Motorola Boot Services app from the Play Store before the new boot animation greets them. The folks over at Android Central have also uploaded a video showing the new boot animation in action -:
The code inside the APK suggests that this boot animation will run from today until January 6th. This is the first time that an Android OEM has updated the boot animation of their devices to reflect the holiday season.