Motorola officially supports unlocking the bootloader of the Moto G2 (XT1068) smartphone. (You will lose your warranty though.) The best guide I found to unlocking the bootloader of the XT1068 is here.
(Note that my phone is the dual-SIM XT1068, not the single-SIM XT1064. It was running Android 5.0.2 (Lollipop) when I tried this. You will need a Windows computer to perform the following steps.)
Since the forum posts keep changing, here are the steps that worked for my phone at this time:
The unlocking process will wipe your data and apps. So if you need any of the data, back it up to the cloud.
Download the Minimal ADB and Fastboot tools installer from here and install it. After installation, you will be able to invoke it from the Start menu by using its name: Minimal ADB and Fastboot. It will open a command prompt with the current directory as
C:/Program Files (x86)/Minimal ADB and Fastboot/
Download and install the Motorola Device Manager from here. This will install the Motorola drivers needed for this operation.
Fastboot the phone: first, power it off. Next, press the power and volume-down for 5 seconds and let them go. You will be dropped into a boot menu.
Connect phone to your computer using a USB cable. The USB status on the phone boot menu should change to connected after you do this.
Open the Minimal ADB and Fastboot prompt. To get the data required to unlock, try this:
fastboot oem get_unlock_data
This will print the data string required to obtain the unlock key for your phone. Concatenate the multi-line output together, this is the data string you will need to provide to Motorola to get the unlock key.
Go to the Motorola bootloader unlock website here. You may need to create a login. Follow the instructions, paste the unlock data string and click to get the unlock key. It will be immediately emailed to the address you provided.
In the ADB prompt, check if your device is connected:
Now unlock the bootloader using the unlock key you got:
fastboot oem unlock type_your_unlock_key_here
Your bootloader is unlocked! XT1068 will display a Bootloader unlocked warning screen. From now on, you will see this display whenever you power down or power up the phone. You will be able to boot back into Lollipop now.
Tried with: Windows 10 x64