While modern C++ is pretty nice, I still think D and Rust have completely eaten its lunch. At this point I think the only thing C++17 does better than D or Rust is brand recognition. :P
The advantage of C++ is that it borrows C's syntax. You can't beat the simplicity of C's syntax. I don't really care about C++ backward compatibility with C, but so far, when I read go, rust, and sometimes D, it looks alien and a little too complex to me.
Not saying C++ templates are good enough, but I think there are not many languages out there with a concise, limited syntax like C or python. Being easy to read and easy to learn is the most important aspect of a programming language. There is python, which really excels in this particular aspect of what makes C great, but I can't really think of any other language which is as much easy to read or comes close.
D is a good contender, but not everybody needs high level, multi paradigm and speed, and are ready to learn something new, especially when you can't reuse C++ libraries.
D on Windows is surprisingly pleasant though.
Rustwin's law: As discussions of C++ grow longer, the probability of a comparison to Rust approaches 1.