Hi everyone.
This is for people interested in developing some kind of plugin to create an automatic masking based on the wall thickness.
I have no idea how to do that as i have no programming skills 
. But i believe this can be done as it works in some online services such as shapeways.
I figure this kind of algorithm could be implemented in Zbrush by a plugin looking for topology thickness. This could result in a masked area which could be easily polygrouped or polypainted for after editting.
I do love 3D print exporter plugin as it really gives the real measurements for the Tools. And i think there are the real scale and measurements that could be used for this wall thickness test. So may be this new plugin could have an slider to set the minimum wall thickness you want to be masked.
Hope some body find this options usefull
Cheers