It isn't an either this or that kind of situation. You're imposing a false dichotomy on the issue.
Just because we don't want to stick with the good ol' reliable 1000-years-to-break-down pollution like the way you put it, doesn't mean we should jump on the first promising path we see. Or else you might find yourself in ten years with all the seagulls dead or something.
If you define far future as far enough then it may well be coal or oil. The same thing with lignin is what made coal - it was a hydrocarbon "plastic" of its day that bacteria hadn't figured out how to consume.
Of course if we assume a remotely industrial era progression of advances oil reserves may be near-worthless. Why dig down say fifty feet for enough oil to fill the shelves of a Walmart camping section?
