First, humans exchanged commodities. You could eat it, burn it for energy, modify it to create tools or jewelry. You exchanged something useful for something useful.
* It was energy.
Then, humans exchanged commodities for gold. You couldn't eat it or burn but it was still possible to modify it.
* It was poor energy.
Then, humans used papers checks or bank notes. It wasn't very useful, but you still could burn it during a very cold winter.
* It was very poor energy.
Now, we wants to use Cryptocurrencies. You can't do anything with it.
* It is not energy but proof of destruction of energy.
Something looks wrong. We should exchange potential energy, not destroyed energy.
Currencies will always be currency. Although time could past by and differ its principles but in terms of its definition it wil probably be as is. As a lot of things could probably change knowing that change is the only one that is constant, paradox but true and somehow continuong to be what it is. This is why some definitions stated where just in addition to what was the usual things about currency that we do know.