Let's start with TCP.
TCP is an abstraction layer over IP, creating the abstraction of reliable, ordered, guaranteed data delivery -- over an unreliable network, which does not guarantee that any given packet will arrive, much less which order it will arrive in, if it even does arrive.
That abstraction is called a "Connection".
But connections come with a high maintenance overhead.
The network stack must check periodically if a connection is still active, must periodically send out keep-alive packets on connections that are, must allocate and deallocate memory for each connection's buffer, must order packets when they come in in each connection's buffer, and must do I/O to whatever subsystem(s) communicate with the network stack, etc.
Speeding up that infrastructure would mean rethinking all of that... Here are some of the most fundamental questions to that thought process:
1) What new set of criteria will constitute a Connection -- on IP's packet-based, connectionless nature?
2) Who will be permitted to connect?
3) How will you authenticate #2?
4) Where (outside NIC, inside NIC, computer network stack, ?) will you perform the algorithmic tasks necessary for #2, #3?
5) What are you willing to compromise for faster speed? E.g, you could use raw datagrams, but not only are they not guaranteed to arrive, but their source can be spoofed... how do you know that a datagram is from the IP address it claims to be without further verification, without the Connection (and further verification of the Connection level, like SSL/Certificates,etc.)?
In other words, rethinking TCP/IP brings with it no shortage of potential problems and security concerns...
It might be faster to simply make the NIC cards faster, as the article talks about...
Or have the Clients or Server software be more selective about what data they send or receive... or what they accept as Connections, from whom, and why...
That is, maybe it's not a speed problem... maybe it's a selectivity problem...
Still, I'm all for faster hardware if DARPA can realize it. :-)