From: Tom Herbert <redacted>
Date: Mon, 29 Apr 2019 16:15:11 -0700

Extension headers are the mechanism of extensibility for the IPv6
protocol, however to date they have only seen limited deployment.
The reasons for that are because intermediate devices don't handle
them well, and there haven't really be any useful extension headers
defined. In particular, Destination and Hop-by-Hop options have
not been deployed to any extent.

The landscape may be changing as there are now a number of serious
efforts to define and deploy extension headers. In particular, a number
of uses for Hop-by-Hop Options are currently being proposed, Some of
these are from router vendors so there is hope that they might start
start to fix their brokenness. These proposals include IOAM, Path MTU,
Firewall and Service Tickets, SRv6, CRH, etc.

Assuming that IPv6 extension headers gain traction, that leaves a
noticeable gap in IPv4 support. IPv4 options have long been considered a
non-starter for deployment. An alternative being proposed is to enable
use of IPv6 options with IPv4 (draft-herbert-ipv4-eh-00).

"Assuming ipv6 extension headers gain traction, my patch set is useful."

Well, when they gain traction you can propose this stuff.

Until then, it's a facility implemented based upon wishful thinking.

Sorry Tom, I kept pushing back using trivial coding style feedback
because I simply can't justify applying this.