Coming next month, the new update for Classic is hitting early, as it was initially supposed to hit in early 2020 alongside the Blackwing Lair raid. However, via the forum post the team mentioned they "detached" the Battlegrounds from the other content release to satiate players who are eager to dive in.
"Warsong Gulch and Alterac Valley will open in WoW Classic simultaneously on all realms the week of December 10. At the same time, Elemental Invasions will occur in Kalimdor, with Blazing, Thundering, Watery, and Whirling Invaders appearing in Un’goro Crater, Azshara, Winterspring, and Silithus respectively.
We’ve been following the deadly deeds of the Classic community closely over the last week as the Honor system sparked an impressive amount of World PvP on PvP realms, and we’re excited to see what might transpire over the next three weeks. Nonetheless, like many of you, we can’t wait to charge into some battlegrounds, so we’ve detached this content unlock from the plan we previously announced. Blackwing Lair and Darkmoon Faire are coming in early 2020."
Battlegrounds will come to World of Warcraft: Classic on December 10th. You can check out our review of the Classic experience here.