I'm in the middle on the long term poly question - the mechanicals have certainly proven themselves by now, but 30 years is about where I'd expect to see even the best of poly's/plastics start to dry, haze, flake, become brittle or deteriorate in some way.
If the polys exhibit any shrinkage it may pull away from the metal frames causing it to all loosen internally?
I'm curious what they'll be like at 75 or 100... our kids will find that out.
Nylon, the frame material of Glocks, has been around for over 75 years. It was invented in 1935. The properties of the material (including how they change with age) are well understood.
This should be good for a chuckle...
"...plastic poses special problems for landfills. Most plastic is not biodegradable, which means it does not break down to its simple component parts. This means it remains present in landfills indefinitely."
So while the rest of the world is worrying that disposable plastic items will last forever in landfills, the gun community is worrying that durable goods made from high-strength, high-quality plastics will become useless in a generation or two.