What is interesting is that with the release of Java 8, a lot of Scala early adopters and cutting back their investment in Scala in favor of Java (for exampled LinkedIn). This is despite the fact that Scala is widely used in production, has a killer app in Spark, and allows pretty seamless use of the Java library.

Now compare this to Rust. Rust also provides an 'improved' language in the same space as C++ utilizing LLVM. However, what is interesting is the nature of the improvements. The biggest feature of Rust is the memory safety. However, the memory safety is not a productivity improvement as more of a safety improvement. Unlike garbage collection where you just do not have to think about memory allocation issues, Rust forces you to think about ownership and mutability. That same exact thinking will allow you to pretty much get the same memory safety in C++ using unique_ptr and shared_ptr and const. The difference is that the compiler makes you think about it in Rust. Much like Scala inspired the adoption of features for Java, you can see C++ adopting pretty much the borrow checker as a tool - see Herb Sutter's talk at CppCon 2015 - https://www.youtube.com/watch?v=hEx5DNLWGgA .

As the experience with Scala shows, the adopted features of the established language do not have to perfectly match the 'improved' language to convince people to migrate back to the established language. The adopted features just have to be in the ballpark. I think the new C++ tooling will be in the ballpark in much the same way that Java 8 is in the same ballpark as Scala and remove much of the impetus for moving to Rust from C++.

In addition, Rust is not as well positioned as Scala. Scala is actually deployed in production and has a killer application. Rust has no major production deployments of which I am aware and no killer application (the equivalent of Spark). In addition, while Rust can interface with C libraries, Rust cannot interface with C++ libraries unlike Scala which can interoperate with the Java standard library.

Rust has some brilliant aspects just like Scala has some brilliant aspects. However, C++ (like Java) is not sitting still but has been incorporating the best ideas. In addition, when people choose a system language, they are inherently conservative because the system they are creating will typically be long lived and mission critical. If you are writing something that you hope will power your company for the next 20 years, do you want to go with a language created and driven by Mozilla with no major use in production, or with the language that powers Google, Microsoft, Apple, and Facebook?

Here is what I recommend. Learn C++11/14/17. Learn Haskell to really open your mind to what is possible. Learn Rust to learn about the borrow checker. Then apply what you have learned to make yourself a better C++ programmer. Some of the best, most insightful C++ programmers I know are people who are actually well-versed in other languages, especially functional programming languages.