One of Nexus main selling points was the openness the devices provided. They could even run non-Google made OSes, which was ironic considering that the devices were made partially by Google themselves. The Pixel lineup replaced Nexus with the same promises of being able to OEM unlock the bootloader, however, Google's latest flagship pair was haunted by a bug preventing users from doing just that.
Google has updated the issue tracker showing that the issue has been fixed, however, it's not as easy as just unlocking the bootloader after all. You need to factory reset your device, after updating it to the latest software available, then make sure you're connected to the internet while setting it back up.
This shouldn't be too painful for the majority of users, as unlocking your bootloader wipes your device anyhow, and that's something you should already know if you're planning on unlocking it.
This whole issue brings another issue to light, and that is bootloader bugs. While this bug is not dangerous, a bug could show up later on which could brick your device, rendering it unusable. Messing with your device is always dangerous, no matter if you think it is or not, so keep that in mind.
Nonetheless, it's good to see that one of the main selling points of the Pixel 2 is actually working now and everyone should now be able to do as they please with their devices.