So you could insert your own little sketches into your listings you mean?
That could be useful for quite a number of things, I had never thought about it myself.
Anyway, no matter what development language you use, there always seem to be independant editors available to write the code so there would be nothing stopping you from coding your own IDE for your favourite language if you were really determined, or maybe even modifying an open source one.
You never know, the idea of diagrams within source code might catch on
