Why poison its only limited to PvE?
It could be a nice improvement to spears, powder bag, traps, and some melee weapons to apply poison.
You can use a poisoned spear to apply the poison debuff (may be it will need to be lowered, specially in the critical resistance), and then use your primary weapon to finish an easy target.
It can even be different kinds of poison, like one focused on DoT, other applying the current debuff, may some other that reduce movement speed or AP+.
I know that can be annoying to carry antidotes on the top of bandages and other healing stuff, but maybe some of the healing items can be merged, like having a medikit that heals and cure bleeding at the same time, other that cures poison and heal, and some bandages dipped in antidotes that cure bleeding and poison at the same time.