This link was posted today by one of the Rhino developers - There is a prototype plug-in for "explicit history" modeling in Rhino 4. The little video shows the history tree being a type of node-based system with a visual interface. It is only the first baby step, but at least this looks very promising. I'm happy that McNeel is finally working to develop constraint based modeling in Rhino...
http://en.wiki.mcneel.com/default.as...nMainPage.html
shorty