[EvenThisAcronym]

> Rust came to be to address the issue with security and there is not really an alternative.

What does Rust have to do with security? It's not even compliant with any modern security standards (at least not that I'm aware of).

> I have no idea what I would use D for.

This makes no sense. D is a general-purpose language, just like Rust, Nim and Go (and it does concurrency better than Go, IMO). It just happens to be the best general-purpose language that I've ever used. The language gets out of your way and lets you focus on solving problems in the domain you're working in.