There are seven layers according to the OSI model. The TCP/IP model simplifies this into "above layer 4", layer 4, layer 3, and "below layer 3". In practice, TLS/SSL is an implementation of the session layer (layer 5) with other protocols run on top in the application layer. The data link and physical layers don't map particularly well to LLC, MAC, and physical transmission technologies but they serve as a reasonable approximation. The presentation layer (layer 6) doesn't really exist but neither did the session layer until a need for encryption inside of TCP came along. Onion routing could be argued to be another session layer technology. The real world is messy and simplifying it into four (or five) layers of nested protocols puts TCP/IP on a pedestal. So take the title with a grain of salt.

The original article argues that cryptocurrencies are a layer of protocol, wrapping those above it. Looking at NameCoin, it isn't an argument that should be dismissed out of hand.

While the OSI model is commonly referenced it's pretty rare to see the Internet Protocol Suite. In this case, I'd argue the author could have said we need an alternate transport protocol but with his argument I don't think you can say that crypto-currencies aren't just another application (as noted elsewhere).

Bonus points for the Snow Crash quote though - one of my favorite authors!

I find the concepts of session and presentation layers within the OSI model to be quite nebulous today, especially when you try to map TCP/IP concepts onto them - because it's not a like-for-like comparison.

I think I prefer the '5th layer' concept - an extension of the TCP/IP stack between 'Transport' and 'Application'.