I would love either a combine for Archfiend DoomLord and Archfiend Deathlord, or some way to obtain a version of Deathlord that can give 25%+ class and rep boosts. Possibly a quest that requires obtaining both, to even start, which at the end would reward you with an armor with a 45% damage boost to all tags, and a 25-30% boost to xp, rep, etc. This would ensure the farm would be worth it, other than to flex, for the extremely hardcore out there like myself.
I would also want to recommend a weapon pairing for this armor, with my reasoning being that i am someone who enjoys having "one set" that i use for all content.
This weapon would grant 65% more damage to all monsters, and would require obtaining Necrotic Sword Of Doom in order to farm for, and would hopefully have a dual option via weapon reflection, or even possibly paying many nulgath resources, in addition to a weapon reflection.
My reasoning for choosing these values, 45%, and 65%, is because pairing them together would make them marginally better than the optimal weapon-armor pairings we currently have.
Please have mercy if I've rambled