It seems interesting, so far I only took a quick glance at it.
It reminds me a bit of the modes stuff, in these blog posts:
What seems nice to me, about these modes is that they are orthogonal to the types and thus the type system doesn’t become overly complex. But so far I have only observed it from the outside and not played with these ideas / experimental features. OCaml with these additions seems nicer to me than Rust, but I guess that doesn’t say a lot since I haven’t really used either of them.