I've seen about six people go through this journey. Burning waste veggie oil, or even biodiesel, is considerably more annoying and labor intensive than merely filling a car. Unless this changes, it's unlikely to scale in the way you indicate.
The real threat is actually blends that use a small amount of biodiesel mixed with rock diesel. These can be burned in any engine, and there is so little food oil (animal and vegetable) compared to the demand for liquid fuel, that this practice can easily lead to the kind of effects you describe.
The real threat is actually blends that use a small amount of biodiesel mixed with rock diesel. These can be burned in any engine, and there is so little food oil (animal and vegetable) compared to the demand for liquid fuel, that this practice can easily lead to the kind of effects you describe.