The iPad, with the Apple Pencil is pretty much there. It’s actually amazingly good. I have terrible handwriting, and it doesn’t seem to have a problem with it.
If anyone ever tried using a Newton, there was a series of Doonesbury comics[0] about its awful handwriting recognition.
I got pretty good at writing with the Newton, but it was me adapting rather than the Newton understanding my natural handwriting (which is fairly neat given my parents are both teachers).