Keep raising the level cap with no changes to the leveling experience up to that point. This leads to ever-lengthening leveling ramps that make it extremely difficult for new players to get to current content. That's because each expansion adds another several dozen hours to how long it takes to get from the start to being able to play with friends in the endgame. (Final Fantasy XIV has this problem to some degree, even though it's nowhere near as old as WoW.)
The Shadowlands can be seen as a shadowy version of the physical world, and can be routinely visited as a spirit when player characters die. Governed by the Covenants, the four ruling realms of the Shadowlands are Bastion, Ardenweald, Revendreth and Maldraxxus (although countless others exist), which serve as the main setting of World of Warcraft's eighth expansion.
It's hard to get a sense of an entire World of Warcraft expansion from 30 minutes of play. In my short demo, I recreated my main (a Beast Mastery Hunter) and played through the introductory quests from the Bastion zone, a heaven-like plane from Azeroth's afterlife. The minute-to-minute gameplay very much followed the formula of modern WoW questing, with a variety of tasks like challenging specific enemies to duels, helping craft things in timed minigames, and of course, killing 10 rats (well, not rats, but they might as well be).