I'm more of a R7RS kinda guy but I appreciate this, especially the types. Scheme allows for extremely non-linear memory access which means you necessarily need dynamic memory management and garbage collection. IMO once you're to that spot, there's little reason to stick with Rust, though it being the implementation language is interesting in itself. That being said, there are battle tested Scheme implementations out there that have fantastic FFI APIs that would probably work just as well if you don't mind a small bit of C to glue things together.