Author here. Sorry, I abandoned this two or three years ago. Please look at this in the context of a project done several years ago and never completed. (I do ML research these days -- you can see my blog here: http://colah.github.io/)

Julia Longtin took up working on ImplicitCAD a few months ago. I'm not sure how much she's progressed with it.

Honestly, I no longer believe ImplicitCAD was the right approach to the problem, or that there's even as much of a problem as I originally thought. In particular, the system ImplicitCAD uses to represent objects, a variant of f-rep (http://en.wikipedia.org/wiki/Function_representation) has issues. (f-rep is awesome, I just tried to have my cake and eat it too with some trade offs, and thought I was being really clever! :P)

After ImplicitCAD, I worked with Rob Gilson on a SVG/WebGL constraint-based modelling tool, mech.ly. We got some neat stuff working, but never got to a point where we wanted to release things. I'm pretty persuaded this is the right direction to go.

I learned a lot from both projects. I also matured a lot intellectually. For example, I now review academic literature before diving into solving hard problems! :)