Ractors are experimental in Ruby 4.0, and so is Kino. This is software for experimenters, but one can dream of Ractor support in Rails.
github.com/yaroslav/kino
A high-performance Ractor web server for Ruby 4.0+: Rack 3-based, with a Rust Tokio/Hyper front-end and Ractor-parallel Ruby workers and threaded fallback mode. - yaroslav/kino