It will take a good engineering / feasibility study to answer that question. You'll need a couple of pilot plant designs (proof of concept and scale-up), then preliminary production plant design with good cost estimates of all of those. Then an analysis of the collection of the plastics from consumers and production plants and a cost estimate for that. Then life-cycle estimates for feedstocks, catalysts, maintenance, power, cooling water, waste disposal, etc.
I used to do that in a prior life for new power technologies. It's not a simple nor a cheap effort.
Of course, you can always start with a cocktail napkin at the local watering hole...
