Those specialized network cards have ASICs that parse network packets and don't need additional memory to do their job. You can easily build a fixed-size hardware register to hold an IPv4 packet header, for example.

But a "high level CPU" is all about operating on high-level objects in memory, so your question becomes, how do you store a linked list in memory more efficiently than a RISC CPU? How do you pointer chase to the next node faster than a RISC CPU? Nobody has figured it out yet, and I agree with the article, I don't see how it's possible. CPUs are already general-purpose and very efficient.

Probably! Everything runs on economics. Network and graphics accelerators did just fine—but then they were (or became over time) high-volume opportunities. Volume drives investment; investment drives progress.