Blizzard plans to open the Arathi group in all areas of World of Warcraft next week.
Forum posts show Blizzard’s intentions,

"With the opening of the World of Warcraft Classic PTR, we have a test environment in which we can examine some of the content used in World of Warcraft Classic.

In particular, we plan to open the Arathi basin in all regions during the week of March 10. At this point, we will also launch the "Battlefield Holiday" system.

We plan to open Zul’Gurub in April and launch the legendary Nightmare Dragon.

We will notify you as soon as the content is published. ""

You can also catch the legendary cape in World of Warcraft. There are 15 step-by-step instructions that you must follow to obtain the layer. In case you missed it, here it is,

Accept the initial mission "The Return of the Black Prince" (tribe) or "Unwanted Advisor" (alliance). If you are authorized, you should receive this task automatically. * *
Meet Magni in the Heart Room to continue the introductory mission.
Enter Magnum's original room with Magni and accept the challenge of waiting.
Meet King Phoris in Ramkahen and end the raid on Uldum.
Meet Magni Bronzebeard in the ventricle and tell Roar about your new corrupt object as part of the Curious Corruption mission.
Talk to your mother about the damage to your personal belongings to unlock the cleaning of the Titanic. While this will unlock the ability to clean items, do not clean them now. ** **
Meet Magni in front of the Mogu’shan arch on top of Kun Lai.
Travel to the land of knowledge in the valley of eternal legends, talk to Lorewalker Cho.
Head to the misty town to meet Rajani and end the attack in the Valley of Eternal Life.
With the Nalak'sha engine, enter the Eternal Flower Valley with Magni to face the challenges ahead. (If you've already done this to another character, you can talk to Ra-den to ignore the Narak Engine scene.)
Go back to court with Bin Laden. (If you talk to him again, he can take you there directly).
Talk to Magni to complete the next set of missions, then escort to the Uldum origins room to face what's coming ...
Talk to the confusing organization of the Chamber of Commerce of the Heart and complete the task "Start the descent".
Enter Blackwing's descent into Blackwing Mountain in Burning Steppe, accept the challenge and expect a damaged bonus.
Return to the ventricle and talk to the roar to complete the mission and receive a new legendary cover that identifies the layer of Ashracamaz.