Week 2 (next week): Legion Assaults begin, first PvP Brawl becomes available
Week 3: Chapter 5 of the Class Order Hall campaign unlocks, which activates new followers, new Order Hall upgrades, and class-specific World Quests
Weeks 4-11: Ongoing story pieces unlock, leading up to the eventual opening of the Tomb of Sargeras raid, and the ability to earn Class Mounts
Looks like we've got over two months until the next raid opens up. 11 weeks puts it releasing on June 13th, give or take a week.