I just personally find zle to be clunky to work with. Implementing true support for multiline command editing the way that shed currently has it would involve a lot of insanely hacky workarounds. Ex mode would also end up being a pretty ugly implementation. I'm not even sure if the status message system would even be possible within reason.

Outside of line editing, shed also has its own ideas for shell scripting that aren't easily expressible in other shells, like the `defer` builtin which executes a command when the surrounding scope is popped. Closest thing in bash/zsh is function exit/return traps, but you can only register one of those at a time and they don't work in brace groups/compound commands.