I've been working on a project with similar goal to RLSL, called Emu. It's a procedural macro that automatically off-loads portions of code to run on a GPU. Here's a quick example...

  #[gpu_use]
  fn main() {
      let mut a = vec![0.2; 1000];
      let mut b = vec![0.3; 1000];
      let c = vec![0.0; 1000];

      gpu_do!(load(a));
      gpu_do!(load(b));
      gpu_do!(load(c));
      gpu_do!(launch());
      for i in 0..1000 {
          c[i] = a[i] + b[i];
      }
      gpu_do!(read(c));
      
      println!("{:?}", c);
  }

Emu is currently open-sourced as a 100% stable Rust library and while it only supports a tiny subset of Rust, that subset is well-defined with useful compile-time errors and a comprehensive test suite.

So if you're looking for a way to contribute to single-source GPGPU for Rust, please consider helping expand Emu's supported subset of Rust. The repository is at https://www.github.com/calebwin/emu

I will say that since Emu works at the AST/syntax level, RLSL is of great interest to me because it works instead at the MIR level which allows it to more easily support a large subset of Rust.