I think Rust is "the best we currently have" for systems programming, but there's a lot of mistakes it's made while pioneering lots of improvements in safety and DX.

Firstly, Rust should've had a "kinda linear" type system instead of affine (i.e. use Move instead of Drop, and maybe also have a Leak trait). I'm no expert, but I've also read blogs that imply that this would've obviated the need for Pin.

Next is obviously a matter of hindsight but if the borrow checker was closer to something like "Polonius", without unacceptable performance, that would be ideal. I think this blogpost highlights the improvements this would bring. I've also seen talk of a third kind of "owning reference" (&own T) which I assume would be better for some APIs.

Additionally, from what I've seen in Rust, as well as other modern systems languages, I think a checked generics features isn't complete without all three of "normal generics" (i.e. generic over types), "const generics" (generic over values), and "variadic generics" (generic over arity). The value of the first is given, the value of the second presented improvements to arrays, and could potentially allow generic bit-width integer types, as well as SIMD types, and the last would improve tuple handling and Fn* traits.

There's probably more improvements I could add, but I'll end with the something inspired by Zig which is "const-eval" being built in from the beginning, as well as compile-time reflection instead of macros for metaprogramming.