Yes, this would be very cool, where you start getting sick while near them, if near them to long you could even die.

Ooo but you could also do poison tips on weapons too and even armor for the hand to hand crowd.

Ya this could be cool in so many ways with poisons. You can mix it with drinks or food, weapons.
You could have many different types that allow for animals to fall asleep. Or maybe even have it slow actions down of a player once poisoned. I cant wait for food and these types of things to come into the game. Balancing is always key.

Indeed. It will take a bit of checks and balances to pull it off just right.