Has Annex K been axed yet, and if not, why not?
Sounds like you don't care for Annex K. What don't you like about it?
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1967.htm
(1) runtime constraint handler callbacks are a terrible API.
(2) The additional boilerplate doesn't buy us anything — the user can still specify the wrong size.
(3) The Annex invents a feature out of whole cloth, rather than standardizing existing practices. There are no performant real-world implementations that anyone uses. Microsoft's similar functionality is non-standard.