In an interview with Windows Central, Associate Director Maria Hamilton and Executive Producer Holly Longdale discuss new content for solo and casual players coming in The War Within, from the introduction of Delves to their intent to revamp the Brawler's Guild!
Recognizing that Blizzard has undeserved the casual community, Delves are a new form of world content described as an evolution of the Researchers Under Fire event, replacing the PvP track in the Great Vault in order to create an avenue of endgame content progression outside of Mythic+, Raid, or PvP content that players of any role can do within a shorter span of time, either solo or in groups of up to five.
This evolution of previous expansion features like Torghast, Island Expeditions, and Mists of Pandaria scenarios includes 11 tiers of difficulty to continually challenge players, it's unclear exactly where that target will land. Previous incarnations all promised the same, but inevitably tapered out quickly — lacking enough challenge or variety from one playthrough to the next to create true replayability. Delves intend to safeguard against this by capping rewards at +7-8 so that the final tiers can remain optional challenges, while rotating modifiers affect week-to-week gameplay. There are also plans for a «secret» one-room boss fight Delve to provide an ultimate challenge.