Totally agree here. Find it a little ironic that the thing I most often want to undo, is undo. But it can't be undone! :-)
I accidentally pressed that button often enough that I figured I must be doing something wrong. When I found out what was going on I tried searching ways to customize the keyboard to remove the key or disable it – which lead me to this thread.
Suggestion 1: Remove the key. I thought shake was weird, but at least it rarely happened by accident (for me at least).
Suggestion 2: I like the swipe function for the keyboard that turns it into a mouse. But maybe there's a gesture (up/down swipe?) that could reveal keys that are dangerous when accidentally pressed? Or turn the undo button into a button that reveals double height undo/redo buttons that slide in from the left.
Suggestion 3: Voice activated? "Hey Siri, undo!" :-)
Suggestion 4: Make undo, redo-able? E.g. Shake to redo an undo. (FWIW, This was the first thing I tried).
Suggestion 5: Make the default behavior for the undo button more discrete. The thing completely wipes out entire paragraphs. Maybe have it undo one word at a time or some number of keystrokes (10) at a time or something?
Thanks for considering.