Let's face it: petroleum won't be the feedstock for our polymers forever. I'm not saying when a changeover will occur  but it certainly will occur. There is only so much oil on the planet and getting it will be only more expensive in the future. At some point, alternative sources for monomers will be economically viable.
Hydrocarbon Processing has a top-notch review article of what is occurring in the biorenewables arena.  Fuels continue to be the leading area of development, but it is mentioned that 4 different routes are being developed to create p-xylene - that precursor to terephthalic acid, which is the "T" in PET. PLA is still the leader in bio-based polymers, but options are also being discovered for PE and PVC. The political environment and past failures also discussed. It's worth a look-and-keep.
 I tend to think much further in the future than the worst doom-and-gloom scenarios, but making accurate predictions is not my strength. If it were, I would be rich, retired and really tan.
 Kind weird, huh? This journal is pretty much 100% devoted to processing and refining petroleum, and even they have an article on bio-based feedstocks.