These languages aren't capable of expressing the software that's routinely written in C (inc C++). For example, there's no way to enforce the lifetimes of NaN-b

These languages aren't capable of expressing the software that's routinely written in C (inc C++). For example, there's no way to enforce the lifetimes of NaN-boxed pointers managed by the multithreaded GC in the custom heap of your browser's JS engine. There's certain classes of C's UB that can be addressed, but most of it can never be without neutering C to the point of uselessness.