An all out ban? Catastrophic without a lot of time to prepare, years at least, probably a decade or more. So many people rely on medical devices at least partially made of plastic. Polyester and nylon are in all kinds of things, pretty much all cheaper fabrics. Most shoes have plastic. Lots of plumbing and construction in general uses PVC, even electric wiring is often coated in plastic. All cars, trucks, trains, and airplanes. Nearly all electronics. Weapons of all types, from pistols to missiles.
I think the only way to do it without killing people would be a phased approach that starts with the most common and least essential plastic goods, but even then it would take a lot of time to implement alternatives.
Surely it can be done, but not any time soon and definitely not in the imperial core. I could see China doing it long-term, like a decades-long plan to slowly reduce plastic use in manufacturing, shipping, etc.

