Sadly, D has its own set of problems and design flaws. It's better than C++ in many ways, but still far from Rust in terms of solid foundation in computer science and language design. Frankly, I see no point in integrating it with Rust.
And what do you mean by Rust being weakest in these categories anyway, and why do you think it is? What are "string-first apps"? And how is not adopting inheritance-based OOP a weakness? I think, many experienced programmers, especially those familiar with ML family of languages and otherwise well-versed in different paradigms, will argue that this particular flavour of OOP is more harmful than helpful.
I admit I do not come from an academic computer science background. What I do bring to programming language design, however, is decades of experience in programming, compilers, and being on the front lines doing tech support on them.
In other words, the human factors facet of language design. D does very well as a friendly language from a human factors perspective.
A simple example of this is `+` is commonly used to mean both addition and concatenation, leading to confusion with awkward resolutions. D uses `+` for addition, and `~` for concatenation. It's been working great.
We also regularly correct errors in the design of D.
