The next Xenoblade Chronicles 2 DLC appears to be headed back to the Aegis War, as discovered by the ResetEra user Moosehunter (reported via Destructoid). Of course, it may all be placeholder info, or even red herrings, as data-mined info can be sometimes. Still, this would be likely as it's the first story-based DLC and included in the Season Pass for XBC2. Take a look below as to how it might work:
Drivers (read: NPC companions) are out, and instead you'll be controlling Lora, Addam, and Mythra with their own statlines. It also may provide Blade gifts for the main game, including Shulk. This would all be part of the season pass if you already own it, and the first major story DLC for Xenoblade Chronicles 2 when it arrives later this year.