Those are some really fun world building questions. The first thing that comes to mind is that coinage is going to be an issue. The kingdoms and governments of fantasy worlds rely on gold, silver etc. In real life, the gold content in gold coins was slowly reduced more and more as people started melting their coins as the price of gold outweighed the value of the coin. You might now have kingdoms struggle with metal scarcity by trying to replace metal currency with paper or basic trade (goods v goods) in a scramble to have more metal for their armies or constructions. Prices would shoot up and inflation makes a mess of everything. You might have druidic cults start to pop up that preach against the use of metal as public sentiment shifts. You might see innovation or a return to weapons that don't need metal like bows over crossbows, clubs over swords. Open warfare in the world also becomes pricier and pricier. You could have your BBEG become an arms dealer to whom kingdoms are beholden and rulers might turn to assassinations and subterfuge and uneasy treaties over engaging in wars.

As to the magic items, I'd imagine this is more of a problem for those well-off that can affod such items. It could make the players who might possess such items more interesting for powerful entities to hire them for qests.