Like I said we can already negate poison duration stacking so further changes on this aren't necessary. If you tried to kill dbaal with poison damage in the latest patch (excluding punishers\graveyard\SoD etc.) you will see it behaves a lot like as if you're damaging him with any other element - he only takes a small amount of damage per hit.
My point about poison appeal is this. Currently poison damage/skills are arguably the best at killing trash mobs in the game. Poison skills have always had really good tuning since Laz's time and nowadays the fact that they are limited against some bosses lead to trash mobs having lower resistances to poison compared to fire/cold/lightning. So naturally you want that power to translate to killing bosses. But if we nerf punishers\graveyard\SoD etc. so they actually behave like normal spells (requiring spell damage & pierce stacking to be good) and then take 20-30% off every other poison passive/skill then poison's "op appeal" is no more and the only thing left is the convenience of you not using a secondary skill for single target.
And about enfilade: mana regen is only a good stat for mana sustain on characters with big mana pools because of the way the mana regeneration formula works. So for a WDM based javazon with a high WDM skill like Enfilade you would want to use mana leech paired with a high phys damage javelin instead.