This is nice and all, but the main issue with UB and C++ IMHO has never been that "nice", modern codebases are problematic - modern C++ in the hands of competent people is very nice, really. The problem is that 90% of all C++ development ATM is done either on legacy codebases full of ancient crap or with old frameworks and libraries that spam non-standard containers, raw pointers, allocate manually, ...

In my experience, introducing modern C++ in a legacy codebase is not that much easier compared to adding Rust to it. It's probably safe to argue that C++03 stands to C++26 almost like K&R C stood to the original C++