The spell called "spiritual projection" or "astral projection" brings the caster to the Twisting Nether instead of the Shadowlands; and the Twisting Nether is also referred as "realm of ghosts". However, both planes don't appear to be related, as Outland is floating on the Twisting Nether, but the Shadowlands can be reached in Outland in The Burning Crusade.
Certain playable races will receive new customization options (for example, humans will be able to customize their ethnicities, dwarves and trolls will gain tattoos, and undead will be able to show varying degrees of decay). The Death Knight class (added in Wrath of the Lich King) is being opened up to pandaren (added in Mists of Pandaria) and to all allied races (added in Legion and Battle for Azeroth); players who pre-ordered Shadowlands received access to death knights for these races with the release of Patch 8.3.0, Battle for Azeroth's last major content patch, on January 14, 2020.
Explore the Realm of the Dead: for the first time ever in World of Warcraft, players will cross into the Shadowlands and experience the wonders and horrors of the afterlife across five new zones—the gleaming fields of Bastion, the scarred battlefields of Maldraxxus, the eternal twilight of Ardenweald, the opulent keeps of Revendreth, and the horrific Maw.