"This document describes a set of source-level tools to communicate
potential future ABI breakage from any library (not just the standard
library) to its users. It does not propose to break ABI, but provides a
mechanism for doing so in an orderly fashion in future C++ releases."
The full document is located here:
https://docs.google.com/document/d/1P1mL1J0rXJlRnLYrcquzLVqE3jPd_IC6uQYnMIE68vA/edit?usp=sharing
"There is great reticence to add new standard library classes"
Is there? I'm not sure I want to live in a world where we add a lot more classes to the standard, if what we have now is the result of great reticence!
The comparison with previous proposals would benefit from references to those proposals.