Hopefully somethings can be considered :
1. Emetic should have more uses like putting it on weapons.
2. Knock-out poison should not use up a whole vial. Maybe 2-3 uses per vial. Thieves with blackjack have no limited uses, and they can keep whacking without much cost involved. Poison thief have it tuff.
3. Have a small air-tight container to contain 4-5 potions, which allows the duration of the vials inside to last longer.
4. Examining a vial will give some duration descriptions like - concentrated (just mixed), normal, diluted, after which the vial evaporates.
5. Looking at a poison weapon should disclose the sticky substance upon it, ie still poisoned.
6. Suggest should work with eat/drink. This will make eat-drink poisons more useful.
7. Concoct antidote should nullify other kinds of poison like spells and prayers.

So far, I believe the thief revamp has been really well thought out and a thief is more like a thief now.