Well, not really. Higher-kinded type parameters are something that requires a kind (typeclass) system in the first place, which D intentionally doesn't have (as D's authors are opposed in principle).
Yeah, I shouldn't have made it read like I was equating the two. What HKT means is that typeclasses, like Monad, can take parameters of higher kinds. But if you don't have typeclasses in the first place (like D doesn't), then you don't have HKT.
I'm referring to what people want when they say they want "higher-kinded types" in Rust. That is: the ability to have typeclasses with higher-kinded type parameters.
I'm well aware that the formal definition of an HKT is just a type with a higher kind, and that's irrelevant to this discussion.
What certain Rust users want to do with HKT can already be done with D (maybe they're LKT's, loosely-kinded types -- you heard it here first!) or, for example, quite explicitly, C++, without type classes, so it's quite relevant.
No, it's not relevant. When people say they want HKT, what they mean is that they want to create typeclasses that abstract over types of a higher kind and only those types, with a type system that can make those guarantees.
Saying C++ has HKT because it doesn't have typeclasses is like saying Python has all of Haskell's type system features because it doesn't have static types. There's a sort of vacuous sense in which it's true, but it's not a particularly meaningful or interesting thing to say.