If something is growing very quickly then saying it hasn't yet dethroned C, so it won't ever be significant seems to me to be a bit brittle thinking. Compound growth and the passage of time - thats what has been underway for some time now.
From what I have seen of D, it provides a C++ without some of the cruft, but without trying to solve other issues with C++-like languages (for eg: usefulness of Algebraic Data Types). Why should someone choose D today over Go or Rust for any project? I have yet to see a convincing answer.
Over Rust: No need to learn new concepts like borrowing
D over Go: D has much better language mechanisms for abstraction and programming in the large.
Go over D: Go has an incremental, mature GC.
Rust and D do not quite target the same application domains (though there's overlap), so it's difficult to compare them. Insofar as they do (D with @nogc and @safe), the tradeoffs become rather complicated.