I didn't read the whole thread; I only read the OP and decided to comment. With six pages of comments in 24 hours, I suspect this might have already been covered, and if so, I apologize for the repetition. But anyway.
It's a complicated answer to a simple question, but here's the short of it:
- Druids in my campaign cannot wear armor made of metal.
- Armor can be made of materials other than metal, though.
- Therefore, armor that is made of non-metal materials is just fine for druids to wear.
So in my campaign, druids cannot wear Half Plate, because it's made of 'shaped metal plates' according to the PHB. But they
could wear a suit of Medium armor made from, I dunno, 'shaped plates' of chitin that were harvested from the shell of a
chuul. That armor would have a base AC of 15+Dex, weigh 40 pounds, and impose Disadvantage on Stealth checks. We just won't call it Half Plate.
So if that druid is willing to put in the work (hunt down a chuul or two, harvest enough chitin, carry it back to town, and hire someone to craft it into a suit of armor), that druid can be the envy of her entire enclave. It's a pretty good hook for an adventure, to boot.
I don't know if it's the right way to do it, and I wasn't in the room when the game designers were talking about stuff like "bounded accuracy" and "rules as intended" or whatever. But my players love it, and the game didn't explode when our druid crafted a breastplate out of the shell of a giant beetle.