Replacing existing unsafe C++ elements with compatible memory safe substitutes[1] might be more expedient. The conversion can even be automated[2] for parts of the code that aren't performance critical.
I'm not a fan of these types of efforts. You could be putting energy into making Rust better. Memory management aside, C++ has become an incomprehensible mess filled with cruft. Rust does much more than provide safety, it provides better abstractions, a better type system, and actual tooling. Building tools for C++ to keep the ship afloat just means we have to deal with writing C++ longer.