Things like web browsers will continue to have millions of lines of C++ code regardless of how successful Rust becomes. It would be a huge improvement for everyone if such projects had a tractable path towards memory safety
As this article discusses, it's not really viable that existing codebases will be able to benefit from safe C++ research without massive rewrites anyway
Yes, absolutely. But it is still easier and more practical for those codebases to write new functionality in a Safe C++ dialect than it would be to use Rust.