There's an interesting parallel here: the system proposed in the post is concatenative, and the undo tree style is, well, a tree. Sort of a Forth v. Lisp thing

There's an interesting parallel here: the system proposed in the post is concatenative, and the undo tree style is, well, a tree. Sort of a Forth v. Lisp thing. Here the big disadvantage of Forth, the implicit stack state, is less obviously balanced by something good. The UX of undo trees could certainly use improvement, it would be great if undo/redo behaved as expected, but any pivot point would automatically pop up the tree view. Then there's cherry-picking, but I have a solution to that. This is in fact the thing I want most from an editor: select a region and then undo/redo changes only in that region. Search and replace tends to work this way, but I've never seen it in an undo/redo system. How many times have you modified a function, broke it accidentally, and just didn't notice and made more changes? So the tests go red, you run a diff, and you see exactly what needs fixing: but you copy and paste out of the diff, because you can't just undo within the offending function.