I don't think that Tor in javascript would improve anything. Tor in golang on the other hand would gain multithreading and ease of integration. It would drop in nicely with the Golang standard library.
A Go version wouldn't improve anything upon the Rust version either. At this scale, Go's simplicity would be a hindrance more than a help, development velocity would suffer compared to Rust. Integration would only be possible in the Go ecosystem, whereas Rust can expose a C API so that Arti can be used (eventually) as the engine for implementations in other languages (Go, Python, JS, etc). Multithreading and overall performance can be better optimized in Rust.
Tor is critical security software with a lot of implementation gotchas. Just like you shouldn't write your own crypto, you shouldn't write your own Tor. Arti is developed by contributors of the original C Tor, I wouldn't go near a Js/Go/whatever implementation from a team with less credentials.
