Maybe the next update with a Mythic only available in the Soulforge.
EDIT: could it be… (!) Spoiler Alert (!) -- [Any Details Provided are Subject to Change] (Part 1) - #3581 by yonizaf
EDIT2: it seems it will be option 2 from @Fourdottwoone: Imp rollover
EDIT3: apparently, Autumnal Imp is already in the chests… so forget EDIT2 