IIUC this is what Profiles are. It’s an opt in source file method to ban certain misfeatures and require certain other safe features.
But then the problem becomes where exactly do you opt-in to this feature? If you do it in a header file then this can result in a function being compiled with the safety profile turned on in one translation unit and then that exact same function is compiled without that safety profile in another translation unit... which ironically results in one of the most dangerous possible outcomes in C++, the so-called ODR violation.
If you don't allow safety-profiles to be turned on in header files, then you've now excluded a significant amount of code in the form of templates, constexpr and inline functions.
Stroustrop, 2023 presentation: https://open-std.org/JTC1/SC22/WG21/docs/papers/2023/p2816r0...
Sutter, 2025 committee paper: https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p30...
Sutter, 2024 blog post: https://herbsutter.com/2024/03/11/safety-in-context/