There's no point. Rust can already be added incrementally in an existing C++ or C project. Like how Servo was in Firefox, or Rust in the Linux kernel.
If it makes you feel better you can rename the Rust language to "C++2.0" but the rewrite process itself will be the same in both cases. You keep expanding the amount of safe code you have within the codebase over time, one module at a time.
For example, one advantage of this strategy as opposed to an incremental Rust re-write is that you would retain a single toolchain, whereas that would require having two.
Anyway, all I can say is that having used both C++ and Rust for many years, I have zero desire to use another C++ toolchain.