I built my own harness on Elixir/Erlang[0]. It's very nice, but I see why TypeScript is a popular choice.

No serialization/JSON-RPC layer between a TS CLI and Elixir server. TS TUI libraries utilities are really nice (I rewrote the Elixir-based CLI prototype as it was slowing me down). Easy to extend with custom tools without having to write them in Elixir, which can be intimidating.

But you're right that Erlang's computing vision lends itself super well to this problem space.

[1]: https://github.com/matteing/opal