That's great ! I have been looking for such a quick online vim experience for quite some time.
A month ago I did find what I consider to be even better : make of any textarea on any page a neovim instance with the firenvim extension (thanks to which I am writing this comment in neovim in my browser!)
It's not even a vim-like experience, it's literally your configured neovim in the browser !
Somehow I haven't managed to get it to the front page (this is not my creation but I am a big fan since I have been looking for this for so long)
I even get autocompletion and all coding niceties in the little code playgrounds that are all the rage in nowadays tutorials
Love Firenvim. Although I think there are different usecases for a vim-in-a-website and something like firenvim (or emacs-anywhere[1], which is what I'm using nowadays, after I've crossed over to the evil side) - as you can use vim-in-a-website from another machine without any setup, like vscode.dev for vscode, for instance. Self-hosting something like this could mean you could add your dotfiles, or maybe even have the website be able to pull a .vimrc from a publicly available dotfile repository, that would be pretty neat.