The ratio is about 16.4 now. The Economist last updated the Big Mac index in July, giving a U.S. price of $4.80. So 19.2 burgers cost $92.16, about 17% higher than the current price of a barrel of oil. I project a burger price next December around $5, and a win for me if the oil barrel price is under $97 or so.
I think you stand a reasonable chance. I read that the Saudis are sick of cheap oil, and that, paradoxically, their way to do away with it is to make oil cheaper. That is, if they increase production to the point that the price drops below the threshold where it's no longer viable to extract shale oil, then they can seriously damage that industry (which is pretty much all American). This isn't so easy, I wouldn't think, as it would take an extended period of losing money to really make the industry players pack up and go home. How long of a period is anyone's guess (if this theory is even true), but I would imagine they would have to bleed for a while.