And if you think about it some of the commodities are almost equal to currency. Take Gold/Silver for instance. Their value is almost same everywhere, depending on different charges and purity ie but what I mean is one can sell/buy it almost everywhere. Same is with Bitcoin. Even if it is not given the currency status, you'll still be allowed to trade it for whatever you want.
Yes if we talk about gold, one can sell it for fiat and even it can be exchanged for some other metal. For example jewellers sell it to the customers for INR and they directly interchange gold for other metals like silver with other dealers.It is done in a way that 1kg of Gold is exchanged with some kg's of silver. Similarly Bitcoin can be sold for fiat and even it can be exchanged with some other cryptocurrencies by adjusting the price accordingly like 1 Bitcoin can be exchanged with about 200 Litecoins. I hope I am clear with my point.