Money has never needed 'cryptography' or any kind of meta-layer obfuscating technology to implement a fundamental monetary property (such as fungibility). Any monetary medium that works will have self-generating fungibility - like the cash drawer or gold's low melting point.

If I melt down 10 gold coins to make a gold bar and then use that in a transaction, I'm not "hiding" the fact that I'm making the transaction. The fungibility does not come from any form of encryption, but rather from the fact that gold coins could be combined from 10 distinct "inputs" into one indistinct "output".

It's an inherent part of cryptocurrencies that that is possible - which is why they make an almost perfect monetary medium. Darkcoin / Dash levers that property without changing the fundamental characteristics of the blockchain. I'm not saying that a cryptographic approach like cryptonote isn't interesting or potentially useful in many cases, but I'm saying it's not necessarily the optimal solution to bitcoin's fungibility problem from a monetary point of view.