I suppose the proof-of-stake coins act a little like stock, in that one gets to contribute to the 51% that writes the rules of the network, but I take your poin

I suppose the proof-of-stake coins act a little like stock, in that one gets to contribute to the 51% that writes the rules of the network, but I take your point. Ultimately, crypto-coins are a new type of financial instrument that don't fit cleanly into either currency or commodity (given that they're not exchangeable for something tangible). Owning BTC is subjectively stock-like, in the sense that its present value is based primarily on network effects, and its future value is highly uncertain.