I wonder if they explored using a Gc like https://github.com/Manishearth/rust-gc with Rust. I think that probably removes all the borrow checker / cycle impedance mismatch while providing a path to remove Gc from the critical path altogether. Of course the Rust Gc crates are probably more immature, maybe slower, than Go’s so if there’s no path to getting rid of cycles as part of down-the-road perf optimization, then Go makes more sense.