Never going to happen, the most efficient plant for making biodiesel is rape seed, what is called canola oil. All you need to do is squeeze it to remove the oil, and you have a produce that can be used as animal feed left over.
What about hemp?
The most efficient plant is probably genetically engineered algae, which is where most of the research work on biodiesel is going on today.
Soybean oil, however, is more or less a byproduct of milling the soybeans into cattle feed.
I notice that this article plays fast and loose with the difference between biodiesel, which actually works and doesn't necessarily have to drive food prices up, and corn-based ethanol, which gives lower mileage in engines not engineered for it (= most of them) and is guaranteed to drive food prices up.