It's structure and behaviour much more resembles a commodity than it does any other asset class; it is basically digital gold. The CFTC agrees and considers itself the responsible regulator.

With the important distinction that it's not an economically useful commodity. Sure, the CFTC regulated it, because their remit is one of the broadest. So you could call it a commodity by default. But it's not like you could make jewelry or breakfast cereal from Bitcoins in the same way you could use commodities like gold or wheat. So it's arguably more like a gambling instrument than any real commodity.

Really, though, I think the closest financial match is a private currency: https://en.wikipedia.org/wiki/Private_currency

These are illegal in most places because they historically have caused a lot of problems without much in the way of redeeming value: https://en.wikipedia.org/wiki/Banking_in_the_United_States#1...

Gold has a value beyond what it is worth (and which aids to its value): you can use it as a jewellery.

Digital currencies can be used via computers and networks while physical currencies such as banknotes and gold requires sneakernet.