I have found the metal armor restrictions to be rather disruptive, we have largely ignored this at my tables. To start with what defines "metal armor"? Is studded leather metal? Almost all middle age shields are primarily wooden IRL, maybe some bucklers were metal, but no other metal shields existed. In the far east IRL there was wooden armor that would most approximate half-plate, breast plate or splint mail.
Also in terms of story or theme, if a Paladin can go against his oath and become an oathbreaker or an asimar become fallen, why can't a druid wear metal?
Just a stupid rule IMO and it does not seem to add much flavor IMO since he can swing a metal scimitar and seems to have no problem adventuring with the guy wearing chainmail. Also as a tree-hugger I would find it somewhat silly to say - "sure you can cut down that tree and make me some armor, but no metal"
What do you think?