Add just a couple more features and you’ll have ed(1), the standard text editor.
Seriously though, I’ve been playing with a Replica-1 Plus, and it’s made me remember that almost every microcomputer had BASIC installed, which generally included a very terrible line editor. planck allows you to insert lines between other lines - in BASIC convention, you’d number lines with multiples-of-10 in case you needed to insert any hotfixes later! Really fancy BASICs would have a RENUMber command that would also update your GOSUB/GOTO targets. And they all generally supported a LIST command, unlike planck.