100% agree with that, with one nuance thought... copy&paste. Just a nuance of course, that's clumsy to move things around. But I like the idea of small specialized things being able to communicate. Maybe even the OS should be one of those small things...
Also, that would be cool if apple was opening the keyboard ui as a plugin... Maybe that's done already??

Ok, proper link (not the only handwriting app available by the way):
http://www.ubitouch-studio.com/ijot

It always strike me that before doing handwriting recognition, one should have a decent... handwriting app!
I was recently pleased by stuff like http://www.ubitouch-studio.com/ijot, kind of original.
But the bottom line: start with beginning!!