As it stands, in Act 3 the player, on behalf of the Black legion, sides with either Kymon’s Chosen or Death’s Vigil, ostensibly to form an alliance in taking on the Chthonians and Aetherials, but nothing really comes of it.
With the addition of the final part of act 4 I always expected to see members of the allied faction fighting alongside the Black Legion. I think it would be nice to add some KC/ODV fighters alongside the Legion NPCs in the Plains of Strife and Necropolis, and would add some sense of resolution.
Of course, the may just be a bunch of self-interested jerks
Maybe the feature didn’t make it for release? Or it was gated behind difficulty/reputation?
I remember that the final faction quest was choosing a deployment in the localization files. Though the changelog mentioned a fix that prevented factions from spawning in the Necropolis? I did one or two Log runs but I didn’t meet anyone.