I agree it would be nice to be able to edit (and move within previously typed) text. But I'm not sure how much work this would involve. For now the game interprets repeated keystrokes when you keep a key pressed, such as when you want to delete several previously typed words by holding down the backspace key. To me, that's already a major improvement in text input - even though it's still quite basic if you compare it to a proper text editor. But unsurprisingly SDL was never designed to work like a text editor. ;-)