Greedy people go to Revendreth.
But, there could be a Broker realm, where entities trade and showcase their captures on an auction, sort of thing, for the highest bidder.
That is considered a sin. so, most likely, they go to Revendreth.
The sins of Revendreth of each Medallion seems to be based off of the Roman Catholic Seven Deadly Sins, and likewise the Ritual of Absolution in the Halls of Atonement seems to be a spin on the Sacrament of Reconciliation (Confession), given a soul must willingly confess their sins and want redemption in order for their sins to be released from them properly.
Elementals go to the Elemental Planes.
Dragons, as seen with Ysera, probably go to the different realms of the Shadowlands. If i had to guess, Neltharion went to, either, the Maw or Revendreth, and Malygos to Bastion.
Dragon Isles would, probably, be the next expansion.
As for Arcane, it seems Bastion represents it but, i don't know how much it delves into the whole time and illusion of arcane. To me, it feels more like a Priest covenant.
If you, already, have Halls of Valor and Helheim, what more could they add?