I threw the code together last night. It's running on cloudflare backed by an S3 static file, so shouldn't be capacity issues
It was only tested on Firefox, as a basic proof-of-concept. AIUI, chrome et al offer similar functionality but maybe the API is different
It may also take a few minutes to find and connect to the websocket, I think CRA webserver maybe only binds to one client at a time, so maybe it would pick up the connection after a webpack-dev-server reload or two.
I have at least 3 create-react-app and one next app running. I even ran a quick websocket server on port 3000 just to see but nada.