What I understood from your article is that you're mostly exploring 1) the possibility of opening up the dev tools to locally-installed applications like SublimeText2; and 2) the integration of jsFiddle-like apps within DevTools.
Please correct me if I misunderstood.
What I'm asking about is creating an in-browser API for a website to interact with the dev tools. Obviously, this would require a very thorough review of the risks of having such an API from a security perspective (and how users can opt-in in a transparent and well-controlled manner). That being said, I am still hoping!
If this is already in the books, then Hooray! I can't wait to start experimenting.
I hope I didn't come across poorly, because I really appreciate all the work you've been doing!
So - Firefox exposes a tcp-based protocol (not enabled by default. The user will need to go to a special tool to start the server). It will expose feature like adding break points, exploring the DOM and the CSS rules, and editing content (CSS/HTML/JS).
So external tools can connect to Firefox. But this protocol is not accessible from a page. But we could imagine using a websocket instead of a normal tcp socket, and let the web page connect to ws://localhost.