I don't recall what changed with v3, but sorry for letting you down. Shortcuts are fully configurable since a few releases: https://docs.mitmproxy.org/stable/concepts-commands/#custom-....
If you have specific feedback about where the keyboard UX sucks I'd be happy if you could open an issue on GitHub so that we can take a closer look!
Any plans for a recommended shortcut setup again?
Not writing 30 characters for copy body of a POST request, but fast key bindings.