After reaching Heart of Azeroth Level 65, I was greeted at the Chamber of Heart with two new quests. One of them starts with Kalecgos who sends you to the Twilight Highlands. There, a Vermillion Holdout scenario requires you to reduce the enemy threat from the Void-Twisted invaders.
After defeating Vexiona, Alexstrasza visits the Chamber of Heart to empower the Heart Forge with Tempered Scale of the Scarlet Broodmother. This adds the Crucible of Flame power.