Not Daniel, but I've ported a typechecker from PHP to Rust (with some functional changes) and also tried working with the official Hack OCaml-based typechecker (a precursor to Flow).

Rust and OCaml are _maybe_ prettier to look at, but for the average TypeScript developer Go is a much more understandable target IMO.

Lifetimes and ownership are not trivial topics to grasp, and they add overhead (as discussed here: https://github.com/microsoft/typescript-go/discussions/411) that not all contributors might grasp immediately.