Wow, the article nailed the UX.

On the implementation side, I think the article implies that you might need to model the edits by Operation, rather than State? Otherwise, the cost of the undo scales O(N) of the content size, which is not viable.

It works well for Git, which models content by State, using Structural Sharing. But Git has built-in delta compression so the memory footprint is roughly O(1) per operation. I don't think implementing this on the web for a <textarea>, or [contenteditable="true"] is a "minimum" effort.

Challenges I can think of:

1. DOM api exposes state, not operations. You need manual diffing

2. When applying the operations, you need to manually restore cursor positions

3. CJK language IME might inject unwanted intermediate states that must be ignored