C, unlike C++, does not really force new versions onto you, even if dependencies begin using them. That said, Linux switched to C11. Newer versions of C will gradually be adopted, despite the incompatibilities this causes for C++.
As for WG 14, they incorporated numerous C++isms into C. While you claim that they did not go far enough, I am sure you will find many who would say that they went too far.
> I very much doubt it, when someone decides to make full of use of recent ISO C on a C library header file.
I have tested this WRT _Generic as it was a concern. It turns out that GCC will accept it on older versions, which permits compatibility. You might feel that this is wrong, but that is how things are right now.
As for WG 14, they incorporated numerous C++isms into C. While you claim that they did not go far enough, I am sure you will find many who would say that they went too far.