Which, to me, suggests three things:
1) There was a Mind Flayer enclave somewhere in Avernus
2) We will be revisiting both Avernus and those cold peaks (putting that "cold resistance" and "robe of summer" to good use and becoming a truly ultimate weapon).
3) (very excited about this last part) the MC and the party will be able to travel between planes on their own at some point, as long a member of the party is already there. We know that Gale has a quest connection to the Astral Plane, Wyll to Avernus, Lae'zel to that weird timeless plane, and I'm assuming that Astarion's master lives in a Ravenlofty demi-plane. This jumping into the Abyss with your friends could be foreshadowed with all those feather-fall jumps into the Underdark.
Jumping planes is not uncommon in Baulder's gate games and I really like this idea. Maybe the Planar Sphere will play a role? I would not feel like they were recycling old ideas if they brought it back in as a way to get to Avernus/Other Planes. I mean it works very similarly to the Nautaloids.
