The latest version of Stud.io supports 13 flexible parts (including string with stud on ends) but sadly rubber bands aren't available yet, which is a shame as they were an important component in my "Professor Branestawm's Invention For Peeling Potatoes" MOC.
The latest version does though fix the problem I had with "missing bricks" when I used the Stud.io photoreal renderer on models that had been created by my ColouredVoxel2LDR script. You can see there are quite a few "holes" in the model on the left, but the model on the right has all the bricks present.