He's referring to how the language and it's ecosystem will evolve from this point forward in comparison to the C++ ecosystem. In addition, the programs that are there should be just fine. There is a lot of room for advancing the Rust compiler to generate more efficient routines from the same code. The Rust compiler, after all, is not taking full advantage of all of the available compiler information. A significant volume of information is simply discarded at the moment. C++ compilers don't have the same degree of headroom for possible future optimizations.