(It seems I mistakenly responded only to a personal e-mail, sorry, responded now to everyone in the list with updates).
So here are the news:
I've created a module called (ice-9 generic-hash-tables), which is similar to SRFI-125, and used it to implement SRFI-69, (RNRS HASHTABLES), SRFI-126 and SRFI-125. Since SRFI-125 depends on SRFI-128, I've implemented it as well. My public repository already has SRFI-128, I'm just finishing some tests with SRFI-125 and, once they are done, I'll push it as well.
The module (ice-9 generic-hash-tables), is quite usable and all exported procedures are documented. I've created tests for it and also ported standard tests from SRFI-126.
Now, I see that 'libguile/hashtab.h' code keeps track of the number of elements in hash tables, but the field is not visible from Scheme. Can that be changed? Then generic hash tables wouldn't need to also keep track of the number of elements (like SRFI-69 currently does) and that would simplify its code.
Besides, what about creating new versions HASHX-* procedures that accept an equivalence procedure instead of an assoc procedure? Perhaps prefixed by 'NEW-' or post-fixed by a '*'.
I've also found inconsistencies between SRFI-125 and it's reference implementation and standard tests. I've implemented according to the specification - so, for instance, HASH-TABLE=? checks if the equivalence function of both hash tables are the same and HASH-TABLE returns an immutable hash table.
Code is public and suggestions are always welcome :)