The point about interaction with undo in a digital inking app is interesting. Seems like with ML handwriting recognition, we could create a handwriting "text editor" instead of a drawing app that understands the semantic structure of the text and operates at that level instead of the individual stroke level.

I had some friends who worked on this for a while but didn't get far with it. It turns out it's tricky to design a general purpose system that adapts to users' handwriting idiosyncrasies and is fast enough to work in real time with handwriting with sufficient accuracy.

Some of that work is still visible in the ChromeOS virtual keyboard handwriting mode, but it's very limited - one line at a time. https://cursive.apps.chrome/ (the built-in note-taking app on Chromebooks) has some interesting inking gestures for manipulating written words, but doesn't have any semantic-level understanding.