I asked 2 years ago, and i was told it was not feasible. I escalated, still no-go, it was a "deep" problem. And they pointed to the IETF saying no on the above drafts as reason to not dig into the microcode or whatever to fix it.
Ok, so that implies that it is burned into hardware and as it is ASIC-based hardware and not FPGA, they can't reprogram the hardware with a code update (one of the advantages of FPGA-based hardware).
Cisco is just one example. The fact is it will likely not work in cell phones, home gateways, windows PCs, Mac's, .... I understand some progress has been made... but choose your scope wisely and pick your battles and know that the weight of the world is against you (cisco and msft)
I don't think I had general usage in mind, more along the lines of the "middle 4" in NAT444 that will be rolled out in many networks to conserve IP space.
@George
Please don't speculating on when Cisco or Microsoft will support 240/4 on this list. Ask your account rep, then report back with facts. Arm-chair engineering accounts for too many emails on this list.
The usage I have in mind would be transparent to the end stations and, frankly, someone who produces provider gear and CPE that can take advantage of that space is going to have a great selling point. There is some gold under there for someone. 240/4 is a great big "dig here" sign if they want some of it.