Null safety is orders of magnitude simpler than memory safety. Kotlin is a null safe language by default. Java is infamously not. Anyone who has worked on a mixed-language Kotlin project can tell you how quickly null safety becomes a pain once guarantees break down - and that’s in a language where these issues are flagged instantly and you can “fix” the problem in a couple of characters! Mixed memory safe/unsafe codebases would be a nightmare in comparison.
Also, C++'s ecosystem consists of deeply entrenched libraries with ancient codebases. Safe C++ might be useful in a decade or two if library maintainers could be pushed to make the switch (good luck with that, if it’s half as much of a paradigm shift as Rust), but by then there will probably be multiple competing language features that claim to solve the same problem. It’s the C++ Way™.
As much legacy code as has been written in C++, I’d think a total rewrite might be better ironically, in terms of passing on important institutional knowledge, to the extent large-scale production codebases are concerned. Attacking it bit by bit (pun not intended) might even take longer than just ripping things up and starting anew.
