Every new finding about how many particles slough off, and get breathed in or ingested, it makes me wish we were still using metal, wood, and glass, for packaging.

I mean... maybe? There are a host of environmental costs to those as well. Certainly, the nice thing about plastic is that its cheap to mold where as metal and wood and glass take a lot more energy to manipulate. The problem is that its too cheap, and so it gets used far in excess of its long term utility.

I think the number one consideration is scalability of production.

Sure. Which is why I'm not holding my breath. But new materials can be useful even if they aren't cheap.