[boomlinde]

RFC2369 from 1998 is "very new"? Funny. I guess it's either a matter of perspective.

Adoption of it doesn't matter insofar that you can use the same link in the body as a fallback, which was part of my suggestion.

"ESPs" don't care because cumbersome and convoluted multi-step unsubscribe is a selling point for the majority of people who use such systems. They have moved from simple mail based unsubscribe which was the norm for years.