Rust is addressed to some of the shortcomings of those. This implies there would a competitive advantage of doing systems programming in Rust, if it succeeds in addressing them.
Calling C++ a single language is like calling Chinese a single language. The various dialects share characters and that's about it. :)
C++ is at least 3 fundamentally different languages over the course of 20+ years. The C++ you would write to the current standard looks vastly different from the C++ you wrote even 10 years ago which itself looks different from the C++ of 10 years before that.
The problem is that even if you only write the modern stuff, you must understand the older stuff as your libraries are often written in it.
Rust overlaps with C/C++ and even with Go. Go was initially trying to be a replacement for C/C++, but hasn't succeeded, because it is too high level. Rust on the other hand looks very promising in that area, which requires low level access but also desires safety.
I wouldn't say Go hasn't succeeded. Maybe not as a general replacement for C/C++. But still lots of new applications that would most likely have been written in C/C++ a few years ago are now popping up in Go (unix daemons, commandline tools, ...).
Go has succeeded in its niche (distributed systems). There are real jobs opportunities in Go, in the major tech hubs.
Funny thing is. Everything that is done in Go could be done in Java. Go is succeeding because lots of dev despise Java (related to the entreprisey & the usual culture of java companies).
As well as the fact that Go runs markedly faster and lighter (memory) than Java, and without needing to worry about JVM versions. We've been slowly migrating services and the statically compiled binaries are truly amazing for ensuring it will run. Not once have I encountered an 'it runs on my machine' situation.
The distributed systems have already moved to Go (when it's not Java/C# :D).
The system programming is done in either C or C++. (Depending on history and availability).
The oldest stuff and/or most constrained is stuck with C. They're struggling to have anything moved over to C++. Rust is entirely out of question.