I think the easy and quick answer is no. That particular defence will still exist, because the crown prosecutor must show there was a voluntary consumption of alcohol. If they, as the defence, bring in evidence that vodka was slipped into some drink they had and that they were unaware of it, and that's what caused the impairment, they can still bring that evidence forward, because it goes to whether or not they voluntarily consumed the alcohol—or the drug, for that matter.
On June 19th, 2007. See this statement in context.