[Snake]

Perhaps everytime you use a void skill you get a stack of a void poisoning status, that deals rank based void damage per turn.
Using any void assassin skill other than Fray, cutthroat and veiloff should increase the void poisonings strength, Veiloff which puts your void essence collecting off would also now serve as a way to shrug off the void poisoning in return for off-lining most of the classes skills.

That could also work, it would also give the 'poisoning' aspect. But that sounds a bit too specific too. Mostly because uhhh, there's no other way to use Void for now, rather than Void Assassin, and even then it's not really that vast and variant. (Only two spells and a ghetto Blink).
Maybe when we get another Void-based class, that could be implemented as a drawback in exchange for reducing drastically the recoil damage? (Or completely nullifying? Maybe, I'd be super down for it.)

Your idea is pretty neat, though what's pushing me into agreeing, but at the same time holding me back is the 'poison' aspect (again).
We already have Poison itself as a damage source. Meh. Sorry. :/