As a language, C++ is used in many different niches, because it allows such low-level control of the machine. However it has many problems around the edges, because it was essentially hacked ontop of C. D is designed to get around these problems, and provide a better OOP langauge. So it lacks some low-level control that C++ has, which you require for for a JIT, which is used in V8. So you'd want to stick with C or C++ for something like V8.

There are also two other recent languages designed to replace niches of C++: Go in latency-sensitive, real time systems, and Rust in systems programming. Rust is quite interesting though, since it introduces many data-safety concepts from function programming into an imperative language.