TCP/IP offload engines, or TOEs (fully implemented in hardware) have existed for a while now, in high-end NICs and of course proprietary implementations (like a comment noted, for HFT). I worked on 1G and 10G implemenations for ASICs over 10 years ago.

Some information here: https://en.wikipedia.org/wiki/TCP_offload_engine

Here's one FPGA vendor targeted towards finance apps with a 40G TCP/IP endpoint (but there are many more): http://algo-logic.com/40g_tcp