With the latest Patch 10.1 Embers of Neltharion PTR build, the 10.1 campaign is now available for testing. We played through the campaign to bring all the details.
WARNING: Patch 10.1 Embers of Neltharion spoilers ahead!
Note: Cutscenes are not available on the PTR, usually being replaced by Captain Exposition explaining what you are supposed to see for each cutscene.
You will receive the quest when you first log in Patch 10.1.