I'm not sure that I understand correctly - are you suggesting that people use Rust as an additional layer between Python and C++?
For single threaded applications, as fast is the goal. There is potential for it to be faster due to stronger restrictions around pointers.
Multithreaded code is slated to be faster mainly because rust provides safety for patterns that would be difficult to do right in C++ (see servo css handling).
That is to say, you could do the same thing in C++, but getting it right is harder to do.
The same environmental conditions don't apply to other software and it's perfectly possible to write blazing fast multithreaded software in C++. In fact that's SOP.
Mostly regarding using BLAS etc in Rust rather than C++. It seems a little pointless as the unsafe nature is within the underlying code, so it only santises input/output.
Adding a thin wrapper over an insecure library won't magically make it secure. That's why pure Rust or pure Swift versions of various algorithms and functionalities are worth so much - guaranteed memory-usage correctness.