Even if there is no new C++ project ever, there is tons and tons of legacy products that needs to be maintained (they are not all going to be rewritten, just as the old cobol projects aren't) and C++ is a deep language that really could benefit from extreme knowledge (a const rvalue reference? wtf).
Rust may fail, but it is probably worth learning some of the ideas - maybe you could use those ideas in your C++ projects?
Oh I've spent years working with Haskell and work with Rust right now! And I absolutely love diving into the pros of awesome type systems. I've actually worked with Golang, F#, Scala, Typescript, Java, C#, C++, Python, and probably a few others (all professionally, as in I've shipped something to prod) over the last few years.
I used to love this but now I'm getting burned out with it all and want to learn a language in more depth.
Rust may fail, but it is probably worth learning some of the ideas - maybe you could use those ideas in your C++ projects?