The C committee (unlike the C++ committee) usually only considers proposals which have implementations to show. And the more real-world experience there is with

The C committee (unlike the C++ committee) usually only considers proposals which have implementations to show. And the more real-world experience there is with the extension, the better. Also consider that this extension is designed in a way that existing code can be annotated without requiring drastic changes, and that it has been designed to remain ABI compatible. A 100% watertight solution most likely requires new language features (or even a completely new language like a "Rust--") that would violate both of those requirements.