Preventing coins from being melted down is crucial for a town to be managing their monetary supply. Governments in real life make it illegal for exactly the same reason. Besides which, in order for coins to be properly convenient, they would lose their quality and which metal they're from even. All those little annoying hassles with homogenizing your coin supply from earlier worlds needs to die for this to work.
Forged coins are a neat realistic concept that would completely undermine the safety of a currency. Due to how the game world and real life differ, especially with regards to the lowered risk of crime ala vidya game, this would make coins far less used. We don't need a repeat of coins in previous worlds, if the devs are going to bother working on this the system needs to be 100% reliable.
If it's truly successful, most ingame afk trading would start being handled this way. This would be a great move towards enabling more complex mechanics with regards to coded interactions between players. I do worry about the ability of players to handle currency convertability with just this update alone. But if we had the ability to rent out stalls via currency, and other hermits/villages could also run stalls there I could see it working. This all hinges on the ability of a safe open city to exist though.
It's a pretty intricate mesh tbh.