I have question and an idea:
When the 5th DLC gets released, will the weapons from your packs drop in the DLC or will we have to still use your vials, or maybe some combination of both? I think it would be nice to get some unique items from bosses and quests, or hell, even make Ug-Thak guaranteed to drop 1-2 from the arsenal. Then again, it somewhat negates the rarity of the vial you picked - so if you were playing on Godless and haven't seen a single gun yet, you'd suddenly be drowning in them.
And the idea: what about droppable consummables, like Insta-Healths or Lance Power Cores from the Secret Armory? They could spice things up a bit, but I also feel like they'd be too gimmicky, and I have no idea how difficult they would be to program into the game proper. What do you think?