Timewalking Campaigns

The system-wide leveling changes for Shadowlands are live in World of Warcraft as of patch 9.0.1 and it's a major overhaul.

The way leveling in Shadowlands works, you do 1 to 10 in Exile's Reach or some other starting zone, then from 10 to 50 you either do Battle for Azeroth content or one of the other expansions, from Cataclysm's revamp of Azeroth to Outland, or Northrend, or Pandaria, or even alternate Draenor or the Broken Isles.