Right, since Barrowholm and the Ravager really, really hate C’thon and it’s cultists, and in light of the fact the cultists in AoM don’t seem to have a base they’re operating from, perhaps it’s worth adding in a dungeon like Harrow’s Lab etc unlocked once you get to Honoured status with Barrowholm.
This would also have a side bonus in that it gives the new C’thonian nemesis somewhere else to spawn, since, like Fabius, it’s really restricted where it can spawn.
As for where, well, the Bloodsworn really like hiding up in the hills, and conveniently there’s a currently inaccessible road skirting the edges of Mourndale with hills and mountains behind it. Make access possible via Malmouth outskirts SE section where you could dispel a barrier the Aetherials have created with an item carrying Ravager’s power.