Look at anything we call money and you'll see it has 0 value on its own. As an example, we can't eat, seek shelter or get security from gold. You can say the same about just about everything that we call money. The value is in the trust that someone else will eventually give you something you want or need. In essence, money is transferable trust. So given this, we can use anything as long as we can trust it. Cryptocurrencies can certainly be used as liquid trust.

The big question is what will people trade for it.