Yup, bringing tools like these for drawing better bezier curves in Illustrator would be so so great. :)

I've started making a plugin to help visualise curvature continuity (using the Illustrator C++ SDK). For example: https://i.imgur.com/4dvV4pN.png

The problem I'm facing is I can't figure out how to make it update live as you drag curve control points around. Currently it only updates once you let go.. :-/