I often find myself pining for Warcraft while travelling on public transport or with a few minutes spare. The order table in the old Blizzard app was a boon, but I think another implementation that would boost engagement would be releasing both daily pet battles (in particular MoP and WoD, perhaps with cooldowns between them to replicate open world travel time) and PvP pet battles in the app.
If it’s difficult to consider how a profit could be spun from it, perhaps an exclusive cash shop pet for users of the app.