My suggestion is to add a villager where you can exchange your coins for another type of coin, so if your whole inventory is filled with dark coins you can go to the 'Coin Exchanger' to exchange your dark coins for gold coins and/or for platinum coins. I believe it has been suggested before, but I feel like it's a good suggestion and should definitely be added.
Here's an example of what it could look like: https://imgur.com/a/ksTG7.
Here's an example of what it could look like: https://imgur.com/a/ksTG7.